The present study was based on follow-up data on 1,409 persons interviewed 4 to 6 years after admission to drug treatments in the Drug Abuse Reporting Program (DARP). The admissions to DARP occurred in 1969-1971, and for most persons the follow-up data included 3 or more years after termination of DARP treatment. The focus of this study was on illicit drug use of former DARP clients, taking into accountifandwhenthey reentered drug treatment after termination of DARP treatment. The results showed that a significant drop in opioid and nonopioid (but not marijuana) drug use generally occurred upon entry into other, post-DARP treatments, and that these beneficial effects of treatment tended to continue beyond the end of treatment. Overall, 42% of the sample had no further drug treatment during the first 3 years after DARP, and almost half (42%) of this group used no opioid or nonopioid drugs at all during this time. Comparisons between DARP treatment groups also indicated that therapeutic community clients had the lowest rate of return to post-DARP treatments.