In a two-week double-blind trial l-methadone and racemic methadone were compared for efficacy in substitution treatment for opiate addicts. Before the trial the twenty-six participants had been on stable doses of l-methadone. Patients with evidence of current serious psychological problems were excluded. Patients were evaluated twice a week using a modified FSUCL, physician's withdrawal checklist, self-rating withdrawal scale, and the Beschwerden-Liste (complaint list) according to von Zerssen. Between addicts continuing on l-methadone (n = 13) and those now receiving racemic methadone (n = 13) there were no statistically significant differences. In particular, patients receiving racemic methadone did not complain more frequently of withdrawal symptoms. In a follow-up period of nine weeks after replacement of l-methadone with racemic methadone, there was also no significant increase in complaints about withdrawal symptoms, although six patients needed an elevation of their daily dosage by at least 20 mg racemic methadone.