Sumatriptan, a 5-hydroxytryptamine1 (5-HT1) receptor agonist at enteric neuronal 5-HT receptors, causes a relaxation of the gastric fundus and inhibition of antral contractile activity. The present study examined the effect of sumatriptan on gastric emptying of solids and liquids in humans. In eight healthy subjects the gastric emptying rate for liquids and solids was measured using the carbon-labeled glycine and octanoic acid breath test after subcutaneous administration of placebo or sumatriptan. Sumatriptan increased the gastric half-emptying time of liquids (P < 0.0005) and induced a prolonged lag phase for liquids (P < 0.0005) in all subjects. Sumatriptan increased gastric half-emptying time (P < 0.005) and the lag phase of solids (P < 0.05) in all subjects. In two healthy subjects gastric emptying of liquids and solids after subcutaneous administration of sumatriptan was studied by radioscintigraphy. Radioscintigraphy confirmed the delayed emptying and the prolonged lag phases after sumatriptan. In conclusion, sumatriptan delays gastric emptying of solids and liquids in healthy subjects. Moreover, sumatriptan induces a lag phase for liquids. The mechanism by which sumatriptan alters gastric emptying remains to be studied.