This study compares the responses of opiate addicts at a London drug treatment centre to two outpatient methadone-based detoxification programmes. These involved either a fixed (non-negotiable) dose reduction schedule or a flexible, negotiable withdrawal schedule. In the negotiable condition, subjects were less likely to complete the detoxification programme and the mean reduction in dose achieved by the subjects in the negotiable condition was less than that in the fixed group. There was no difference between groups in programme retention at 6 weeks though subjects who remained in treatment in the negotiable group tended to extend their detoxification period beyond this point. The overall response of subjects in both groups was unsatisfactory. Only 13% of the subjects initially allocated to detoxification or 28% of those who actually started detoxification completed treatment; urine screening showed that heroin abuse was a continuing problem during treatment. The implications of these results for detoxification and drug treatment services are discussed.