Lower esophageal sphincter pressure (LESP), gastric emptying, small bowel transit time and plasma motilin levels were measured in diabetics and normal subjects in order to investigate the disturbances of the alimentary tract motility and the participation of motilin in these motility disorders. Hypermotilinemia was observed in all diabetics with or without autonomic neuropathy. Low response of LESP to tetragastrin found in diabetics with autonomic neuropathy could not be explained by motilin. Gastric emptying was highly correlated with fasting plasma motilin levels and a significantly accelerated gastric emptying observed in diabetics without complications or diabetics with diarrhea was considered to be due to hypermotilinemia. On the contrary, no significant correlation was observed between small bowel transit time and plasma motilin levels, suggesting no participation of endogenous motilin in the regulation of small bowel transit.