Raclopride, a new potential antipsychotic drug, with high selectivity and affinity for central D2-dopamine receptors, was in this first human study administered to 8 healthy male volunteers in single oral doses from 0.1 to 16 mg. Two subjects, known to be slow metabolizers of debrisoquine, were also included. Pharmacokinetics, safety, tolerability, and effect on plasma prolactin levels were evaluated. The maximum plasma concentrations of raclopride (Cmax) and the area under the raclopride curve vs time (AUC) increased proportionally with dose. No deviant kinetic parameters were seen in the slow debrisoquine metabolizers. Only minor deviations in biochemical and physiological safety parameters were found. Raclopride was well tolerated by all subjects at doses up to 8 mg but not at 16 mg because of akathisia. No other extrapyramidal side-effects were recorded. The drug induced a rapid and transient increase of plasma prolactin concentrations.