Consensus on the optimal dosing of methadone in the treatment of opioid dependence has not yet been achieved, with some programs committed to low dose regimens. This paper presents outcome results for 95 opioid abusers who remained in treatment through a stable dosing period in a double-blind fixed dose clinical trial comparing the relative efficacies of 50 (n = 44) and 20 mg (n = 34) of methadone to methadone-free treatment (n = 17). All patients showed improvements over time on measures of psychosocial functioning and psychological symptoms, emphasizing the important role of non-pharmacologic factors in methadone treatment. Furthermore, orderly dose effect relationships were seen, with patients receiving 50 mg of methadone having significantly lower rates of opioid positive urines (36% vs. 60-73%), and self-reporting a lower frequency of heroin use (3 days vs. 11-12 days per month). These results illustrate the dose-related efficacy of methadone in decreasing illicit opioid use and improving drug-related behavior.