The single-dose kinetics of the neuroleptic thioxanthene zuclopenthixol was assessed in 12 healthy volunteers who ingested 10 mg of the drug orally, both on an empty stomach and together with a standardized breakfast of 1840 kj (440 kcal). The serum concentrations of zuclopenthixol were measured by HPLC. Concomitant food intake did not influence the peak concentration nor the time to reach the peak concentration or the elimination half-life of zuclopenthixol, but the AUC values were significantly increased. Hence it seems likely that concomitant food intake enhances the bioavailability of zuclopenthixol, without influencing its absorption rate. The most likely mechanism is that food reduces the presystemic clearance of the drug. As the increase in AUC was only 26%, it is doubtful whether zuclopenthixol has to be administered in a standardized relation to meals.