Chronic pancreatitis (ChP) is the most frequent cause of pancreatogenous diabetes mellitus (DM). This kind of DM is a typical case of acquired insulin secretion deficiency. The group under scrutiny consisted of 122 patients with ChP. The average age of the 88 men was 42.9 and that of the 34 women was 54.4 years. According to pancreatography and to the presence of calcifications the patients were divided into four group by gravity of the morphological pictures at ERCP. The control group of healthy persons was made up of 15 men and 10 women. The presence of glucose intolerance was rated by the oral glucose tolerance test (oGTT) after 75 g glucose. The volume of endogenous secretion of insulin was studied by measuring IRI and C-peptide fasting and after stimulation. To measure the damage of pancreatic exocrine secretion we used function test (Spofagnost-Pankenzan test). In our own group of 122 patients we found decreased glucose tolerance in 72 (59%). 41% were cases of DM, 18% suffered from impaired glucose tolerance (IGT). As the results of stimulated C-peptide tests suggest, practically all patients with ChP corroborated by morphological changes in the pancreatic duct system at ERCP have decreased endogenous insulin secretion compared with healthy persons, and that includes even those normal glucose tolerance rated by results of oGTT We were able to prove a statistically significant relationship between the degree of morphological changes in the pancreatic duct system and the values of C-peptide. The mean values of the Spofagnost test showed significant differences between patients with normal glucose tolerance and DM.