The motor function of the antrum was studied in 7 normal subjects, 4 patients with diabetes without GI symptoms, and 7 patients with diabetic gastroparesis. Both the number of antral contractions and the cumulative antral activity (percent of time during which the antrum contracted) in patients with diabetic gastroparesis were significantly lower than in normal subjects and diabetic patients without gastroparesis (P less than 0.01). Interdigestive motor complexes were observed in all normal subjects, but they were not present in any patients with diabetic gastroparesis. Intravenous metoclopramide did not affect the rate of antral contractions (P less than 0.1), but it increased the cumulative antral activity (P less than 0.001) in normal subjects and diabetics without gastroparesis. Metoclopramide, however, did not alter the rate of antral contractions (P less than 0.09) or the total cumulative antral activity (P less than 0.09) in diabetic patients with gastroparesis. Furthermore, in normal subjects, the action of metoclopramide was blocked by atropine sulfate (P less than 0.003). Bethanechol caused a slight increase in the number of antral contractions (P less than 0.05) and cumulative antral activity (P less than 0.01) in normal subjects. This cholinergic drug caused a marked increase in the rate of antral contractions and the cumulative antral activity in diabetic patients with gastroparesis. Antral contractions and cumulative antral activity were restored by bethanechol to normal values. These findings suggest a variable degree of gastric neuropathy in individual patients with diabetic gastroparesis with functionally intact antral muscles as assessed by their pharmacologic response to cholinergic stimulation.