Intestinal transit was assessed in 25 insulin-requiring male diabetics and 15 healthy controls by measuring the breath hydrogen appearance time after the ingestion of both the liquid and the solid meal containing nonabsorbable carbohydrate. Three groups of patients were studied: A) nine patients without peripheral or autonomic neuropathy or retinopathy; B) nine patients with peripheral neuropathy; and C) seven patients with peripheral and autonomic neuropathy. Eight patients complained of gastrointestinal symptoms, including three with watery diarrhea. Intestinal transit of the solid meal was more prolonged than the liquid meal in normal and diabetic subjects. There was no significant difference in intestinal transit between normal controls and any group of diabetics; however, one-third of the diabetics had abnormal intestinal transit of the liquid test meal (four rapid, four delayed); only one patient with diarrhea had rapid intestinal transit. These data suggest that abnormal intestinal transit is common in diabetics. Altered intestinal transit is not a prerequisite of diabetic diarrhea.