| Mass Park Inc. d/b/a Valet Park of America CT | Other Services | 0 | — | F |
| Mass Park Inc. d/b/a Valet Park of America MA | Other Services | 0 | — | F |
| Mass Park Inc. d/b/a Valet Park of America NY | Other Services | 0 | — | D |
| MASS Precision, Inc. CA | Manufacturing | 0 | — | F |
| Mass Transportation Authority MI | Transportation & Warehousing | 0 | — | B |
| Mass. Dept. of Environmental Protection MA | Public Administration | 0 | — | A |
| Mass. Electric Construction Co. AZ | Construction | 0 | — | A |
| Mass. Electric Construction Co. CA | Construction | 0 | — | A |
| Mass. Electric Construction Co. CT | Construction | 0 | — | A |
| Mass. Electric Construction Co. DC | Construction | 0 | — | A |
| Mass. Electric Construction Co. HI | Construction | 0 | — | A |
| Mass. Electric Construction Co. KS | Construction | 0 | — | A |
| Mass. Electric Construction Co. MA | Construction | 0 | — | D |
| Mass. Electric Construction Co. MD | Construction | 0 | — | A |
| Mass. Electric Construction Co. ME | Construction | 0 | — | A |
| Mass. Electric Construction Co. NE | Construction | 0 | — | A |
| Mass. Electric Construction Co. NJ | Construction | 0 | — | A |
| Mass. Electric Construction Co. NV | Construction | 0 | — | A |
| Mass. Electric Construction Co. NY | Construction | 0 | — | A |
| Mass. Electric Construction Co. RI | Construction | 0 | — | A |
| Mass. Electric Construction Co. TX | Construction | 0 | — | A |
| Mass. Electric Construction Co. VA | Construction | 0 | — | A |
| Mass. Electric Construction Co. WA | Construction | 0 | — | A |
| Massa Multimedia Architecture PC NJ | Professional & Technical Services | 3 | $544,178 | — |
| Massa Products Corporation MA | Manufacturing | 0 | — | A |
| Massac County Fire Protection District IL | Public Administration | 0 | — | A |
| Massac Memorial Hospital IL | Healthcare & Social Assistance | 0 | — | B |
| Massachusetts Acute Care Specialists, PC TN | Healthcare & Social Assistance | 1 | $253,760 | — |
| Massachusetts Association of Health Plans MA | Other Services | 1 | $110,000 | — |
| Massachusetts Bay Transportation Authority MA | Transportation & Warehousing | 1 | $116,735 | — |
| Massachusetts Clean Energy Center MA | Public Administration | 0 | — | A |
| Massachusetts Convention Center Authority MA | Real Estate | 1 | $123,219 | — |
| Massachusetts Department of Public Health MA | Healthcare & Social Assistance | 0 | — | B |
| Massachusetts Design NJ | Manufacturing | 0 | — | C |
| Massachusetts Electric Co MA | Utilities | 0 | — | F |
| Massachusetts Eye and Ear Associates MA | Healthcare & Social Assistance | 1 | $99,000 | — |
| Massachusetts Eye and Ear Infirmary MA | Healthcare & Social Assistance | 6 | $70,786 | — |
| Massachusetts Fire Technologies, Inc. MA | Construction | 0 | — | A |
| Massachusetts General Physicians Organization MA | Healthcare & Social Assistance | 27 | $208,599 | — |
| Massachusetts General Physicians Organization, Inc. (MGPO)/Massachusetts General Hospital (MGH) MA | Healthcare & Social Assistance | 3 | $416,529 | — |
| Massachusetts Institute of Technology MA | Educational Services | 155 | $92,824 | — |
| Massachusetts Medical Society MA | Other Services | 1 | $113,469 | — |
| Massachusetts Mutual Life Insurance Company MA | Finance & Insurance | 40 | $136,275 | — |
| Massachusetts Mutual Life Insurance Company NC | — | 0 | — | — |
| Massachusetts Mutual Life Insurance Company* CT | — | 0 | — | — |
| Massachusetts Port Authority MA | Transportation & Warehousing | 1 | $150,000 | — |
| Massada Utility Contractors, LLC MO | Construction | 0 | — | A |
| Massada, Inc MO | Construction | 0 | — | A |
| Massage Envy AZ | — | 0 | — | — |
| Massage Envy RI | — | 0 | — | — |
