During the treatment of 53 young heroin addicts with intramuscular sulpiride for the prevention of withdrawal symptoms, the emergence of extrapyramidal manifestations involving the head, neck and upper trunk in about 40% of the patients has been observed. These symptoms occurred with sulpiride dosages in the ‘antineurotic’ range (not more than 400 mg daily), which practically never produce such symptoms in patients receiving the drug for other clinical indications. The symptoms appeared soon after the first few injections of sulpiride, and yielded readily to a single or repeated intravenous diazepam administration (10 mg). The possible mechanism involved in the production of extrapyramidal manifestations from sulpiride, and a tentative explanation of why such symptoms are produced by doses of this drug lower than those needed to produce the same effects in nonaddicts, are discus