Ninety-nine patients suspected of having pancreatic carcinoma were studied prospectively for carbohydrate tolerance. Thirty-two patients were proven subsequently to have pancreatic carcinoma; the remainder served as a control group. There was an increased incidence of carbohydrate intolerance in patients with pancreatic carcinoma compared to the control group. Insulin and C-peptide measurements during glucose tolerance tests suggest abnormal beta cell function and possibly insulin resistance as causes for this abnormality. Although factors related to malignancy in general could partly account for the results, a specific factor occurring in patients with pancreatic carcinoma must also be considered as it could serve as a marker for the early detection of this disease.