The effects of administering high methadone doses during detoxification treatment were examined on illicit opiate use and treatment retention in chronic opiate supplementors. Twenty-six applicants to a 90-day outpatient detoxification program who delivered 50% or more opiate-positive urine samples during treatment weeks 2 and 3 were randomly assigned to receive a constant 30-mg dose through treatment week 10 or an increase to 60 mg in week 4 with gradual reduction to 30 mg by week 10. Dosage for both groups was reduced to 0 mg during weeks 11-13. Treatment retention was better for experimental (median = 86 days) than for control (median = 41 days) subjects, but the difference was not statistically significant. In the dose increase group, percent opiate-positive urines decreased from 80% to 62% during the first two weeks of dose increase (t = 2.39, P less than 0.05); opiate positive rates for the control group remained above 80%. A 20% between group difference in percent of opiate positive urine tests persisted through study week 10 in subjects (N = 5 control, 7 experimental) who remained in treatment this long. Although the blind dose increase did improve treatment outcome, we concluded that the magnitude of the effect in this population of chronic opiate supplementors was insufficient to judge the procedure clinically useful.