Propoxyphene napsylate and methadone hydrochloride were each administered under double-blind conditions to 36 outpatients for 21-day heroin detoxification. The initial dosage was 24 mg/day for methadone hydrochloride and 800 mg/day for propoxyphene napsylate. At these dosages, methadone more effectively suppressed the opiate-withdrawal syndrome, and patients remained in treatment longer in the methadone group (P greater than .05). In regard to heroin abstinence, however, results were not statistically significant in either group, as indicated by the number of patients whose urine was positive for morphine on admission and became negative during treatment, and the number who had morphine-negative urine at the conclusion of 21-day treatment. A one-month follow-up of patients showed that more patients given methadone had entered long-term medical maintenance while more patients given propoxyphene were heroin-abstinent. This study indicates that 21-day heroin detoxification, regardless of chemotherapeutic agent, yields a low rate of heroin abstinence.