| 9309 | Marriage bureau | |
| 7523 | Marshals' offices, police | |
| 1543 | Marshmallow creme, manufacturing | |
| 1543 | Marshmallows, manufacturing | |
| 9241 | Martial arts clubs | |
| 1543 | Marzipan (i.e., candy), manufacturing | |
| 3190 | Maser amplifiers, manufacturing | |
| 2029 | Mashers, potato, wood, manufacturing | |
| 2109 | Masking tape, made from purchased paper | |
| 3693 | Masks, fencing, manufacturing | |
| 3311 | Masks, gas, manufacturing | |
| 3693 | Masks, sports (e.g., baseball, fencing, hockey), manufacturing | |
| 9199 | Masonic lodge | |
| 2021 | Masonite® (hardboard), manufacturing | |
| 5143 | Masonry bricks, blocks, tile and stone, builders' supply, wholesale | |
| 2694 | Masonry cement, manufacturing | |
| 7421 | Masonry consultant services | |
| 4520 | Masonry repairs | |
| 4520 | Masonry work, construction | |
| 4520 | Masonry, contractors | |
| 2893 | Masons' handtools, manufacturing | |
| 5143 | Masons' materials, wholesale | |
| 9211 | Mass duplication, motion picture | |
| 2230 | Mass reproduction of pre-packaged software | |
| 3312 | Mass spectrometers, manufacturing | |
| 3312 | Mass spectroscopy instrumentation, manufacturing | |
| 4520 | Mass transit, construction | |
| 9309 | Massage parlours | |
| 8090 | Massage training school | |
| 5231 | Mastectomy prosthesis, retail | |
| 2213 | Master recordings, leasing and licensing | |
| 4540 | Mastic flooring | |
| 2029 | Masts, wood, manufacturing | |
| 9301 | Mat and rug launders | |
| 3699 | Matches and match books, manufacturing | |
| 5139 | Matches, wholesale | |
| 0113 | Mate plantation | |
| 4530 | Materials handling equipment, installation | |
| 5150 | Materials handling equipment, wholesale | |
| 7129 | Materials handling machinery and equipment, rental | |