Who owns MRX
Which tracked institutional funds hold MRX, how they are positioned, and who is buying versus exiting — from SEC Form 13F-HR filings. See MRX company fundamentals →
Ownership as of the 2026-Q1 13F filings (latest filed 2026-05-26). 13F is disclosed up to 45 days after quarter-end, so the most recent quarter fills in over the following weeks.
How the tape is positioned
92 tracked funds added or opened MRX while 36 trimmed or exited it between 2025-Q4 and 2026-Q1 — the tape is split. When large holders disagree on a name, the funds moving first are sometimes ahead of the story.
A prompt to read the filings, not a verdict. 13F is a quarter-end snapshot disclosed up to 45 days late; a fund adds or exits for mandate, benchmark, and timing reasons that have nothing to do with a view on the stock. This is a starting question, not a signal to trade.
Conviction spread
MRX’s largest tracked holder by dollar value, BlackRock, Inc., sizes it at 0.0% of its own reported 13F book, while the median holder sizes it at 0.0% of theirs — a 0.0pp gap the other way — the median holder sizes MRX more heavily than its largest holder by dollar value does.
Book-share is each fund’s reported value in MRX divided by its whole reported 13F book, so it is comparable across funds of different sizes and is unaffected by stock splits. A higher share means a fund has committed more of its book to the name — a starting question about conviction, not a verdict or a signal to trade.
Institutional & insider positioning
Between 2025-Q4 and 2026-Q1, across 206 tracked filers holding MRX, 121 increased or opened the position and 89 reduced or closed it; over the same quarter, there were no open-market insider Form 4s.
This fuses two public signals for the same quarter — how tracked institutions changed their positions and whether insiders bought or sold in the open market. It describes what was filed; it is a starting question, not a verdict or a signal to trade.
New buyers & exits
Funds opening or closing a position in MRX between the 2025-Q4 and 2026-Q1 13F filings, and the largest changes among funds holding it in both. New buyers and exits are counted on fund presence (split-invariant); adds and trims are measured on reported value.
New buyers 21
- VANGUARD PORTFOLIO MANAGEMENT LLC$16M
- T. Rowe Price Investment Management, Inc.$15M
- Hudson Bay Capital Management LP$10M
- COMMONWEALTH OF PENNSYLVANIA PUBLIC SCHOOL EMPLS RETRMT SYS$4M
- Man Group plc$4M
- Militia Capital Management LLC$4M
Full exits 16
- TWO SIGMA ADVISERS, LP$26M
- Portolan Capital Management, LLC$16M
- VANGUARD GROUP INC$15M
- North Reef Capital Management LP$7M
- TUDOR INVESTMENT CORP ET AL$5M
- MILLENNIUM MANAGEMENT LLC$3M
Largest adds
- FMR LLC$104M
- BlackRock, Inc.$44M
- TWO SIGMA INVESTMENTS, LP$40M
- VICTORY CAPITAL MANAGEMENT INC$33M
- SAMLYN CAPITAL, LLC$31M
- PRICE T ROWE ASSOCIATES INC /MD/$26M
Largest trims
- ADAGE CAPITAL PARTNERS GP, L.L.C.$48M
- BALYASNY ASSET MANAGEMENT L.P.$38M
- THORNBURG INVESTMENT MANAGEMENT INC$24M
- DEUTSCHE BANK AG\$17M
- HEALTHCARE OF ONTARIO PENSION PLAN TRUST FUND$10M
- Grandeur Peak Global Advisors, LLC$9M
Institutional holders
One row per tracked fund, largest reported value first. “% of value” is the fund’s share of this security’s tracked institutional value — not of shares outstanding. Rows marked stale are from an earlier filing than the security’s latest quarter — that fund is absent from the newest snapshot (position exited, or reported under a different name).
| Fund | Shares | Reported value | % of value | Quarter |
|---|---|---|---|---|
| BlackRock, Inc. added | 4,389,325 | $196M | 7.8% | 2026-Q1 |
| Capital International Investors | 3,488,093 | $155M | 6.2% | 2026-Q1 |
| FMR LLC added | 3,479,188 | $155M | 6.2% | 2026-Q1 |
| LOOMIS SAYLES & CO L P trimmed | 1,918,622 | $86M | 3.4% | 2026-Q1 |
| PRICE T ROWE ASSOCIATES INC /MD/ added | 1,906,029 | $85M | 3.4% | 2026-Q1 |
| SAMLYN CAPITAL, LLC added | 1,688,877 | $75M | 3.0% | 2026-Q1 |
| TWO SIGMA INVESTMENTS, LP added | 1,681,560 | $75M | 3.0% | 2026-Q1 |
| JENNISON ASSOCIATES LLC added | 1,606,691 | $72M | 2.9% | 2026-Q1 |
| WILLIAM BLAIR INVESTMENT MANAGEMENT, LLC trimmed | 1,566,181 | $70M | 2.8% | 2026-Q1 |
| ALLIANCEBERNSTEIN L.P. trimmed | 1,730,125 | $66M | 2.6% | 2026-Q1 |
| Invesco Ltd. added | 1,335,046 | $60M | 2.4% | 2026-Q1 |
| Grandeur Peak Global Advisors, LLC trimmed | 1,325,195 | $59M | 2.4% | 2026-Q1 |
| VICTORY CAPITAL MANAGEMENT INC added | 1,314,816 | $59M | 2.3% | 2026-Q1 |
| ROYCE & ASSOCIATES LP trimmed | 1,252,790 | $56M | 2.2% | 2026-Q1 |
| Ophir Asset Management Pty Ltd added | 1,246,546 | $56M | 2.2% | 2026-Q1 |
| Granahan Investment Management, LLC trimmed | 1,223,750 | $55M | 2.2% | 2026-Q1 |
| Artisan Partners Limited Partnership added | 1,216,883 | $54M | 2.2% | 2026-Q1 |
| AMERIPRISE FINANCIAL INC added | 954,242 | $43M | 1.7% | 2026-Q1 |
| Allspring Global Investments Holdings, LLC added | 908,596 | $39M | 1.6% | 2026-Q1 |
| STATE STREET CORP added | 873,461 | $39M | 1.6% | 2026-Q1 |
| HEALTHCARE OF ONTARIO PENSION PLAN TRUST FUND trimmed | 729,000 | $32M | 1.3% | 2026-Q1 |
| GEODE CAPITAL MANAGEMENT, LLC added | 726,494 | $32M | 1.3% | 2026-Q1 |
| WELLINGTON MANAGEMENT GROUP LLP trimmed | 655,460 | $29M | 1.2% | 2026-Q1 |
| Qube Research & Technologies Ltd trimmed | 592,606 | $26M | 1.1% | 2026-Q1 |
| WESTWOOD HOLDINGS GROUP INC trimmed | 537,856 | $24M | 1.0% | 2026-Q1 |
| Praetorian PR LLC | 500,000 | $22M | 0.9% | 2026-Q1 |
| Bank of New York Mellon Corp added | 484,524 | $22M | 0.9% | 2026-Q1 |
| GOLDMAN SACHS GROUP INC added | 482,108 | $21M | 0.9% | 2026-Q1 |
| MORGAN STANLEY trimmed | 477,298 | $21M | 0.8% | 2026-Q1 |
| Deltroit Asset Management (UK) LLP trimmed | 449,773 | $20M | 0.8% | 2026-Q1 |
| JPMORGAN CHASE & CO added | 459,049 | $20M | 0.8% | 2026-Q1 |
| THORNBURG INVESTMENT MANAGEMENT INC trimmed | 408,877 | $18M | 0.7% | 2026-Q1 |
| BANK OF AMERICA CORP /DE/ added | 385,026 | $17M | 0.7% | 2026-Q1 |
| Nuveen, LLC trimmed | 380,738 | $17M | 0.7% | 2026-Q1 |
| VANGUARD PORTFOLIO MANAGEMENT LLC new | 363,180 | $16M | 0.6% | 2026-Q1 |
| Swedbank AB added | 354,413 | $16M | 0.6% | 2026-Q1 |
| SEI INVESTMENTS CO added | 354,325 | $16M | 0.6% | 2026-Q1 |
| BALYASNY ASSET MANAGEMENT L.P. trimmed | 346,690 | $15M | 0.6% | 2026-Q1 |
| Russell Investments Group, Ltd. added | 342,988 | $15M | 0.6% | 2026-Q1 |
| ALGERT GLOBAL LLC added | 333,712 | $15M | 0.6% | 2026-Q1 |
| T. Rowe Price Investment Management, Inc. new | 331,243 | $15M | 0.6% | 2026-Q1 |
| MANUFACTURERS LIFE INSURANCE COMPANY, THE trimmed | 310,805 | $14M | 0.6% | 2026-Q1 |
| GLENMEDE TRUST CO NA trimmed | 304,067 | $14M | 0.5% | 2026-Q1 |
| LORD, ABBETT & CO. LLC added | 301,267 | $13M | 0.5% | 2026-Q1 |
| NORTHERN TRUST CORP added | 290,675 | $13M | 0.5% | 2026-Q1 |
| NEW YORK STATE COMMON RETIREMENT FUND added | 238,073 | $11M | 0.4% | 2026-Q1 |
| VOLORIDGE INVESTMENT MANAGEMENT, LLC trimmed | 224,513 | $10M | 0.4% | 2026-Q1 |
| Hudson Bay Capital Management LP new | 224,141 | $10M | 0.4% | 2026-Q1 |
| GLOBEFLEX CAPITAL L P trimmed | 212,125 | $9M | 0.4% | 2026-Q1 |
| Creative Planning added | 208,711 | $9M | 0.4% | 2026-Q1 |
| Engle Capital Management, L.P. added | 200,996 | $9M | 0.4% | 2026-Q1 |
| RENAISSANCE GROUP LLC trimmed | 190,900 | $9M | 0.3% | 2026-Q1 |
| SG Americas Securities, LLC added | 184,519 | $8M | 0.3% | 2026-Q1 |
| CITADEL ADVISORS LLC added | 173,474 | $8M | 0.3% | 2026-Q1 |
| WASATCH ADVISORS LP added | 171,109 | $8M | 0.3% | 2026-Q1 |
| HRT FINANCIAL LP added | 166,121 | $7M | 0.3% | 2026-Q1 |
| Walleye Capital LLC added | 159,830 | $7M | 0.3% | 2026-Q1 |
| STATE OF WISCONSIN INVESTMENT BOARD trimmed | 145,047 | $6M | 0.3% | 2026-Q1 |
| CHARLES SCHWAB INVESTMENT MANAGEMENT INC trimmed | 141,210 | $6M | 0.3% | 2026-Q1 |
| Moody Aldrich Partners LLC trimmed | 139,793 | $6M | 0.2% | 2026-Q1 |
| PRINCIPAL FINANCIAL GROUP INC trimmed | 138,508 | $6M | 0.2% | 2026-Q1 |
| UBS Group AG added | 137,479 | $6M | 0.2% | 2026-Q1 |
| MARSHALL WACE, LLP added | 125,494 | $6M | 0.2% | 2026-Q1 |
| SEVEN GRAND MANAGERS, LLC trimmed | 125,000 | $6M | 0.2% | 2026-Q1 |
| Calamos Advisors LLC added | 110,114 | $5M | 0.2% | 2026-Q1 |
| MACKENZIE FINANCIAL CORP added | 105,976 | $5M | 0.2% | 2026-Q1 |
| Legal & General Group Plc added | 105,584 | $5M | 0.2% | 2026-Q1 |
| COMMONWEALTH OF PENNSYLVANIA PUBLIC SCHOOL EMPLS RETRMT SYS new | 96,439 | $4M | 0.2% | 2026-Q1 |
| BNP PARIBAS FINANCIAL MARKETS trimmed | 94,641 | $4M | 0.2% | 2026-Q1 |
| Man Group plc trimmed | 89,236 | $4M | 0.2% | 2026-Q1 |
| MOODY NATIONAL BANK TRUST DIVISION trimmed | 86,630 | $4M | 0.2% | 2026-Q1 |
| RAYMOND JAMES FINANCIAL INC added | 86,225 | $4M | 0.2% | 2026-Q1 |
| Militia Capital Management LLC new | 85,531 | $4M | 0.2% | 2026-Q1 |
| FEDERATED HERMES, INC. added | 84,904 | $4M | 0.2% | 2026-Q1 |
| RENAISSANCE TECHNOLOGIES LLC trimmed | 80,520 | $4M | 0.1% | 2026-Q1 |
| INTRINSIC EDGE CAPITAL MANAGEMENT LLC new | 80,000 | $4M | 0.1% | 2026-Q1 |
| ENVESTNET ASSET MANAGEMENT INC added | 76,287 | $3M | 0.1% | 2026-Q1 |
| Massar Capital Management, LP new | 73,696 | $3M | 0.1% | 2026-Q1 |
| Jefferies Financial Group Inc. trimmed | 1,000,000 | $34M | 1.3% | 2025-Q3 stale |
| Driehaus Capital Management LLC new | 753,652 | $30M | 1.2% | 2025-Q2 stale |
| TWO SIGMA ADVISERS, LP trimmed | 679,600 | $26M | 1.0% | 2025-Q4 stale |
| WCM INVESTMENT MANAGEMENT, LLC new | 448,113 | $18M | 0.7% | 2025-Q2 stale |
| Burkehill Global Management, LP trimmed | 500,000 | $17M | 0.7% | 2025-Q3 stale |
| Portolan Capital Management, LLC added | 418,745 | $16M | 0.6% | 2025-Q4 stale |
| ARROWSTREET CAPITAL, LIMITED PARTNERSHIP trimmed | 451,618 | $16M | 0.6% | 2025-Q1 stale |
| Fortress Investment Group LLC added | 400,000 | $16M | 0.6% | 2025-Q2 stale |
| VANGUARD GROUP INC trimmed | 399,956 | $15M | 0.6% | 2025-Q4 stale |
| Zimmer Partners, LP trimmed | 300,000 | $12M | 0.5% | 2025-Q2 stale |
| Glenmede Investment Management, LP added | 345,739 | $12M | 0.5% | 2025-Q3 stale |
| Cubist Systematic Strategies, LLC added | 342,574 | $12M | 0.5% | 2025-Q3 stale |
| Ghisallo Capital Management LLC added | 220,600 | $9M | 0.3% | 2025-Q2 stale |
| North Reef Capital Management LP added | 190,000 | $7M | 0.3% | 2025-Q4 stale |
| TUDOR INVESTMENT CORP ET AL | 148,096 | $5M | 0.2% | 2025-Q4 stale |
| SOROS FUND MANAGEMENT LLC new | 124,476 | $5M | 0.2% | 2025-Q2 stale |
| CANTOR FITZGERALD, L. P. added | 140,000 | $5M | 0.2% | 2025-Q3 stale |
| Robeco Institutional Asset Management B.V. added | 127,728 | $4M | 0.2% | 2025-Q3 stale |
| Monashee Investment Management LLC new | 90,000 | $4M | 0.1% | 2025-Q2 stale |
| MILLENNIUM MANAGEMENT LLC trimmed | 82,779 | $3M | 0.1% | 2025-Q4 stale |
| FJ Capital Management LLC trimmed | 81,199 | $3M | 0.1% | 2025-Q4 stale |
Ownership over time
Tracked institutional holder count and total shares held by filing quarter (independent scales). The curated-era tail and any mid-ingest latest quarter are handled honestly — a partial quarter is not drawn as a collapse.
Reading this table
Funds hold the same stock for different reasons — an index fund “holds” almost everything, an active manager sizes a name to a mandate and a benchmark, and each fund entered at its own price and time. Because 13F is filed up to 45 days after quarter-end, every row is a backward-looking snapshot; a manager may have traded since. Share-class siblings (a company’s A and C shares) are rolled up to one line so a dual-class name is never double-counted. Compare like-for-like. A large holder is not an endorsement, and a fund exiting is not a warning — this is a starting question, not a verdict.
About 13F filings
A Form 13F is a quarterly disclosure that institutional investment managers with over $100 million in US-listed equities must file with the SEC. In plain English: it is a snapshot of the long stock positions a fund held at the end of a quarter. It covers long US-listed equities only — not short positions, options, cash, or private holdings — and the funds shown are the large sample we track, not the complete 13F universe.