Plain clothes police officers arrested two people after they observed a drug deal in the area of Errington Street in Chelmsford Sept. 1 at around 10:30 a.m.
The drug deal involved a half pound of marijuana.
The recipient of the drugs, an 18-year-old Sudbury man, has been charged with possession of drugs for the purpose of trafficking and breach of probation.
The supplier of the drugs, a 27-year-old Sudbury man, has been charged with trafficking.
Both were due to appear in bail court Sept. 2.