Opioids and neuroleptics have similar effects in a variety of behavioral, biochemical, and clinical situations. Prolonged treatment with dopamine antagonists is associated with the development of a movement disorder, tardive dyskinesia. Animals treated with methadone for prolonged periods may also develop abnormal movements when challenged with amphetamines. In this study, 243 patients on methadone maintenance were examined for abnormal movements using the Abnormal Involuntary Movement Scale. Methadone treatment alone was not associated with increased abnormal movements. Three patients with abnormal movements were found, but each was also receiving neuroleptics.