In order to study the disposition which is thought to be latent in chronic pancreatitis, we investigated the sweat chloride concentration of 95 normal subjects, 43 cases of chronic pancreatitis, 12 cases of cholelithiasis, 15 cases of peptic ulcers, 16 cases of hepatic diseases and 23 cases of diabetes mellitus with the sweat test, using the method of pilocarpine iontophoresis. We obtained the following results. (1) In normal subjects, the sweat chloride concentration was inclined to rise gradually with age from childhood to adulthood; the mean value of sweat chloride concentration was 30.0 mEq/liter in adults from 20 years old, and the upper limit was about 60 mEq/liter. (2) The mean value of sweat chloride concentration was 60.0 mEq/liter in chronic calcifying pancreatitis; this value was markedly higher than that of control subjects of the same age (p is less than 0.001). (3) The mean value of sweat chloride concentration in cholelithiasis, peptic ulcer and hepatic diseases did not differ significantly from control subjects. The mean value of sweat chloride concentration in diabetes mellitus was significantly higher than that of control subjects (p is less than 0.01), but was significantly lower than that in chronic pancreatitis (p is less than 0.01). (4) It was supposed that some cases of chronic pancreatitis have a congenital disposition toward abnormal secretion of sweat glands and epithelium in the pancreatic duct, resembling cystic fibrosis, and this disposition leads easily to pancreatic disorders when the individual is exposed to various external factors.