1. The pharmacokinetics and pharmacodynamics of prochlorperazine (PCZ) have been studied in healthy young males following single 12.5 mg i.v. and 50 mg oral doses, and during repeated doses (25 mg twice daily) for 14 days. 2. Oral bioavailability was low and an N-desmethyl metabolite was detected. Plasma clearance was high (0.98 1 kg-1 h) and the volume of distribution was large (12.9 1 kg-1) after i.v. dosing. 3. The terminal elimination half-life of PCZ was 9 +/- 1 h and 8 +/- 2 h after i.v. and single oral dosing, respectively. The urinary recoveries of drug and metabolite were low. 4. Accumulation of PCZ and its metabolite occurred following repeated dosing. The half-life at the end of 14 days therapy was 18 +/- 4 h. 5. Postural tachycardia, decreased salivary flow, impaired psychomotor function and a diminished level of arousal were observed after intravenous PCZ. Similar effects, but of lower magnitude were observed after single oral doses. During chronic dosing postural tachycardia and antihistaminic effects were observed, the latter not being observed after single doses. 6. After single intravenous dosing the maximal drug effects occurred 2-4 h after peak plasma drug concentrations for all measures except for plasma prolactin and self-scored restlessness 7. An antagonist action at dopamine (D2), muscarinic-cholinergic and alpha-adrenoceptors is postulated after single doses, with antihistaminic effects during chronic dosing, possibly indicating the presence of an active metabolite.