The objective of this study was to investigate the efficacy of the anticholinergic agent trihexyphenidyl in the treatment of clozapine-induced hypersalivation. Fourteen chronic schizophrenic patients who exhibited nocturnal hypersalivation during clozapine treatment were coadministered trihexyphenidyl (5-15 mg/day, at bedtime) for 15 days. Salivation was assessed by a single-item 5-point scale. A reduction of 44% in the reported nocturnal hypersalivation was observed after trihexyphenidyl treatment. These results indicate that at least some chronic schizophrenic patients with clozapine-induced nocturnal hypersalivation may benefit from anticholinergic treatment.