Mixed D1/D2 dopamine (DA) antagonists, perphenazine (5 mg/kg) and haloperidol (2 mg/kg) induced catalepsy in rats. SCH 23390 (1 mg/kg), a D1 DA antagonist, also produced catalepsy. Co-administration of perphenazine (0.5 mg/kg) and SCH 23390 (0.1 mg/kg), at low doses, produced a marked increase in cataleptic response. B-HT 920, a D2 agonist, reversed the cataleptogenic effects of perphenazine, haloperidol and SCH 23390. SKF 38893 (5 mg/kg) reduced the cataleptogenic effect of SCH 23390 but failed to reverse haloperidol- or perphenazine-induced catalepsy. SKF 38393 (10 mg/kg), however, protected the animals against perphenazine- induced catalepsy. Combined administration of B-HT 920 (0.1 mg/kg) and SKF 38393 (5 mg/kg) enhanced the protective effect of B-HT 920 in SCH 23390-treated animals but not in animals treated with haloperidol or perphenazine. MK-801 (0.025-0.5 mg/kg), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, reduced the cataleptogenic effects of perphenazine, haloperidol as well as SCH 23390. The anticataleptic action of MK-801 was enhanced by scopolamine (0.1 mg/kg) but not by bromocriptine (1 mg/kg) or clonidine (0.05 mg/kg) in perphenazine-treated rats. Unlike B-HT 920 (0.1 mg/kg), SKF 38393 (5 mg/kg) potentiated the anticataleptic effect of MK-801 (0.01 mg/kg) against SCH 23390-induced catalepsy. The above data suggests D1/D2 interdependence in catalepsy and a modulatory role of D1 and D2 DA receptor stimulation on the anticataleptic effect of MK-801.