Interactions of gastrointestinal prokinetic benzamides with 5-hydroxytryptamine (5-HT)3 and 5-HT4 receptors and the relation to their effects on gastrointestinal propulsion were investigated. Renzapride and zacopride potently inhibited 5-HT3-receptor-mediated contractions in the guinea pig colon, whereas RS67506 (1-(4-amino-5-chloro-2-methoxyphenyl)-3-[1-(2-methyl sulphonylamino)ethyl-4-piperidinyl]-1-propanone hydrochloride), a selective 5-HT4-receptor agonist, showed no inhibition. RS67506, renzapride and zacopride all exerted 5-HT4 receptor-mediated relaxation in the carbachol-precontracted rat oesophagus. In mice, RS67506 shortened the whole gut transit time, whereas renzapride and zacopride were reported to prolong it. Gastrointestinal prokinetic benzamides, which are selective for 5-HT4-receptor agonistic over 5-HT3-receptor antagonistic action, may be useful in treating gastrointestinal disorders associated with impaired lower intestinal propulsion such as constipation.