Cyproheptadine-HCl raised the pain thresholds during hot plat test and writhing test in mice and tail flick test in rats, strengthened the hypnotic action by subthreshold dosage of sodium pentobarbital and chloral hydrate. The ED50 were 4.4 (3.2-5.7) and 12.4 (8.4-18.2) mg/kg 30 min after ip cyproheptadine in mice and rats, respectively. The ED50 was 0.14 (0.12-0.18) mg/kg 90 min after icv cyproheptadine in mice. Cyproheptadine po 20, 40 mg/kg and ip 10, 20 mg/kg showed significant antipyretic effects on yeast-induced pyrexia in rats.