The ability of SCH 23390 as compared to haloperidol to produce catalepsy in rats was evaluated in three tests for catalepsy. SCH 23390 produced catalepsy in all three tests with ED50 (mg/kg s.c.) of 0.017 on the vertical grid, 0.023 on the horizontal bar and 0.038 on the 'four corks'. Haloperidol produced catalepsy with ED50 (mg/kg s.c.) of 0.048 on the vertical grid, 0.042 on the horizontal bar and 0.065 on the four corks. Catalepsy by SCH 23390 and by haloperidol was prevented by scopolamine and potentiated by alpha-methyl-p-tyrosine pretreatment. Catalepsy induced by SCH 23390 was also prevented by specific D-2 receptor agonists such as pergolide, lisuride and bromocriptine but not by the D-1 receptor agonist SKF 38393. The results demonstrate that SCH 23390 is potently cataleptogenic and that the catalepsy it produces has a pharmacologic profile typical of that produced by potent and specific D-2 antagonists.