The effect of various classes of serotonergic agents on haloperidol-induced catalepsy was evaluated in male Sprague-Dawley rats. The 5-HT-1A agonists buspirone, ipsapirone and 8-OH-DPAT all potently reversed catalepsy. The mixed 5-HT-1A and 5-HT-1B agonist RU 24969 reversed catalepsy only at the highest dose tested. The non-selective 5-HT-1 antagonist (l)-propranolol did not affect catalepsy. The 5-HT-2 agonist DOI and 5-HT-2 antagonist mesulergine both reversed catalepsy. ICS 205-930 (5-HT-3 antagonist) reversed catalepsy at low doses only. Another 5-HT-3 antagonist, GR 38032F, had no effect on catalepsy. These studies suggest that 5-HT-1A and 5-HT-2 receptor sites are important in the serotonergic modulation of haloperidol-induced catalepsy.