The experience with methadone maintenance treatment by two major New York City methadone maintenance treatment programs using the Dole-Nyswander philosophy is reviewed. After more than 56,000 person-years in treatment over a 10-year period of time, a unit of medical experience exemplified by these two programs is evident. There was a high degree of patient acceptance, a small amount of recognized residual illicit drug abuse, and steeply reduced criminal activities of those patients who remained in treatment. A wide variety of other methadone treatment programs are recognized. Many use methadone differently from those in the present study. The treatment results reported herein may represent a standard by which narcotic (methadone and other) treatment programs can be assessed.