BACKGROUND Pharmacological studies of the enteric nervous system have shown the presence of several subtypes of 5-hydroxytryptamine (5HT) receptor, which might be involved in control of the migrating motor complex. OBJECTIVE To study the effect of sumatriptan, an agonist of enteric neuronal 5HT1p receptors, on interdigestive motility in man. METHODS In 12 healthy subjects, interdigestive motility was recorded manometrically in the upper gastrointestinal tract. In seven subjects blood samples were drawn every 15 minutes for radioimmunoassay of motilin and somatostatin. After two phase 3s of the migrating motor complex, 6 mg of sumatriptan was administered subcutaneously. Recording continued until two more phase 3s had occurred. RESULTS Sumatriptan induced a premature phase 3 in the jejunum after a median of 10 (8) minutes. The duration of the migrating motor complex cycle was shortened at the expense of phase 2. After sumatriptan, plasma somatostatin concentrations were reduced and gastric phase 3s were suppressed, although median motilin concentrations and the occurrence of plasma motilin peaks were not affected. Phase 3s of the migrating motor complex preceding sumatriptan were associated with motilin peaks, while phase 3s after sumatriptan were not. Furthermore, pretreatment with sumatriptan prevented the induction of a gastric phase 3 by the motilin agonist erythromycin. CONCLUSIONS Administration of the 5HT1P receptor agonist sumatriptan induces a premature intestinal phase 3, suppresses gastric phase 3s, prevents induction of a gastric phase 3 by erythromycin, and reduces plasma somatostatin concentrations.