A controlled, double-blind study of the comparative effectiveness of the narcotic antagonists, cyclazocine and naloxone, was undertaken in a metropolitan narcotic clinic offering an abstinence program involving urine monitoring and ancillary counseling services. Seventy male addict parolees were randomly assigned to 6-month treatment with either cyclazocine, 4 mg administered on a daily basis, or naloxone, 500-2,000 mg administered on a locally developed and researched 'contingent' basis, i.e., whenever there was indication of narcotic drug use (daily and contingent placebos were utilized to preserve the double-blind). Criteria of treatment effectiveness included narcotic drug usage, clinic attendance, length of participation in the program, disposition at 6 months, and incidence of side effects. The two subsamples of 35 individuals were similar with respect to relevant demographic characteristics. Examination of comparative effects revealed little to no significant differences between the two groups in terms of measures of program adherence, treatment outcome, and personal and social adjustment. Side effects were more prevalent among cyclazocine patients. Typically, these included moderately severe somatic effects and perceptual and cognitive disturbances.