Twenty-five patients with various forms of dyskinesia were given tiapride for three months. Maximal dosage was 900 mg per day. A double-blind trial of tiapride versus placebo showed significantly better results in the group given tiapride. The forms of dyskinesia which responded best to tiapride were the following: iatrogenic dyskinesia, tics (Gilles de la Tourette syndrome), and chronic chorea (Huntington disease). Patients with complex dyskinesia resulting from neonatal encephalopathy or vascular disease were not improved. The protocol used in l-dopa-induced dyskinesia is described. Changes in dyskinesia and "on-off" effect following variations in tiapride and l-dopa dosage are detailed. An unequivocal, although minor, tiapride-induced parkinson syndrome was recorded in a few patients. No instances of tiapride-induced dyskinesia or akathisia were seen. The other side-effects were either psychic (depression, drowsiness, agitation) or endocrinologic (menstrual disorders, overeating, galactorrhea).