It is known that 5-HT₄ receptors in the colon of guinea pigs show a distribution similar to that in humans. Thus, we examined the effects of mosapride citrate (mosapride) and cisapride, two 5-HT₄-receptor agonists, on colonic motility in conscious guinea pigs implanted with force transducers. Mosapride and cisapride administered intragastrically at doses of 3 – 30 mg/kg significantly enhanced the colonic motility. The enhancing effect of mosapride was antagonized by atropine or GR113808, a 5-HT₄-receptor antagonist, but not by methysergide, a 5-HT₁- and 5-HT₂-receptor antagonist; ondansetron, a 5-HT₃-receptor antagonist; or CP-99994, a tachykinin NK₁-receptor antagonist. In vitro receptor autoradiography showed that mosapride and cisapride inhibit the specific binding of [¹²⁵I]-SB207710, a selective radioligand of 5-HT₄ receptors, in the colon of guinea pigs. These results suggest that mosapride enhances colonic motility through the 5-HT₄-receptor activation in guinea pigs and may be useful for treating constipation in patients with colonic motility dysfunction.