A double-blind, placebo-controlled, crossover trial was carried out in 29 patients with Huntington's chorea to evaluate the effectiveness and tolerance of high doses of tiapride in the management of neurological symptoms. Patients were allocated at random into 3 groups to receive 3 g tiapride daily for two periods of 3 weeks either preceded, interrupted or followed by a 3-week period on placebo. Patients were assessed on entry and at the end of each treatment period using a battery of tests designed to measure choreatic movements, motor skills, recognition and reaction times, and mental state. Twenty-three patients completed the trial; only 2 of the 6 drop-outs withdrew because of drug-related side-effects (sedation and extrapyramidal signs). The results showed that tiapride treatment significantly improved choreatic movements and motor skills and these findings were supported by the objective psychometric measurements. Overall evaluation of effectiveness by the physician and patients indicated the significant superiority of tiapride over placebo. Treatment was generally well tolerated and although there were significantly more reports of sedation and extrapyramidal signs whilst patients were receiving tiapride, these effects were rated as mild in most cases and did not interfere with treatment.