The emetic effects of 5-hydroxytryptamine (5-HT) and 5-HT3 receptor agonists were investigated in the house musk shrew, Suncus murinus. 5-Hydroxytryptamine (5-HT; i.p., i.v., s.c.) and 2-methyl-5-HT (2-Me-5-HT; i.p.) but not 5-hydroxyindoleacetic acid (i.p.) or 5-methoxytryptamine (i.p.) induced emesis with very short latency. Tropisetron (ICS 205-930, a 5-HT3 receptor antagonist, s.c.) blocked the emesis induced by 5-HT (10 mg/kg, i.p.) and 2-Me-5-HT (5 mg/kg, i.p.) with respective ID50 values of 7.8 and 70.9 micrograms/kg. Pindolol (5-HT1 receptor antagonist) and ketanserin (5-HT2 receptor antagonist) were about 100 times less potent than tropisetron. The emesis induced by 5-HT was prevented by surgical vagotomy but not by pretreatment with a combination of atropine (0.1 mg/kg, s.c.) and hexamethonium (10 mg/kg, s.c.). These results clearly indicate that 5-HT is emetogenic probably through a stimulation of peripheral 5-HT3 receptors.