- Machinery, Supplies & Equipment - Business Production Related, Rockville
- Machinery, Supplies & Equipment - Construction & Contractor Related, Rockville
- Malls & Shopping Centers, Rockville
- Management Consultants & Services, Rockville
- Manufacturing, Rockville
- Marine Contractors & Designers, Rockville
- Marriage & Family Counselors, Rockville
- Medical Diagnostic Clinics, Rockville - Clinical Labs & Centers
- Mental Health Specialists, Rockville - Psychologist, Psychiatrist, Psychotherapist, etc
- Merchandise Sales Events, Rockville
- Methodist Church, Rockville
- Mexican Restaurants, Rockville
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- Miscellaneous Government, Rockville
- Miscellaneous Industry, Rockville
- Miscellaneous Professional, Rockville
- Modular & Mobile Homes For Sale, Rockville - Manufactured Homes Sale & Service
- Motor Vehicle, Rockville
- Motor Vehicle Rental & Leasing, Rockville
- Motorcycle & Motor Scooters Dealers, Repair & Service, Rockville
- Motorcycle Repair & Service, Rockville
- Moving Supplies & Equipment Rental, Rockville
- Moving Truck Rental , Rockville
- Museums, Rockville
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