Summary.We evaluated serum gastrin responses to a test meal in normal subjects and diabetic patients with or without vagal neuropathy. Vagal neuropathy was defined as a heart rate variation during deep breathing of < 9 beats/min. Forty-three percent (54 out of 124) of the diabetic patients had abnormal heart rate variation, compared with 5% (3 out of 53) of the normal subjects. Serum gastrin responses to a test meal were examined in 17 normal subjects, 20 out of 70 diabetic patients without vagal neuropathy and 17 out of 54 diabetic patients with vagal neuropathy. Meal-stimulated gastrin levels were significantly higher in the diabetic patients with vagal neuropathy than in the normal subjects, while the findings in the diabetic patients without vagal neuropathy were similar to those in normal subjects, These data suggest that augmented gastrin responses are due to vagal denervation induced by autonomic neuropathy.