We examined the effectiveness of a contingency management program in preventing relapse to illicit opiate use and increasing treatment retention during outpatient methadone detoxification treatment. Twenty male opiate addicts were randomly assigned to an experimental or control group. Following a 3-week methadone stabilization period, men in both groups received identical gradual methadone dose reductions during Weeks 4 through 9 and were maintained on placebo during Weeks 10 through 13. Beginning in Week 4, control patients received $5.00 for providing a specimen twice weekly. Experimental patients received $10.00 and a take home methadone dose for each opiate-free urine specimen but forfeited the incentives and participated in more intensive clinic procedures when specimens were opiate positive. The contingency management procedure slowed the rate of relapse to illicit opiate use. Experimental patients provided significantly more opiate-free urines during the methadone dose reduction in Weeks 4 through 9 than control patients, although the difference between groups was no longer significant during placebo administration in Weeks 10 through 13. In addition, the contingency management program improved treatment retention and reduced symptom complaints during the detoxification. The usefulness and limitations of contingency management procedures for outpatient methadone detoxification are discussed.