The degree of correlation between exocrine pancreatic function and endocrine secretory capacity was examined in 13 chronic pancreatitis patients with secondary diabetes mellitus, 8 chronic pancreatitis patients without diabetes, and 11 healthy subjects. The two parameters were studied under maximal stimulation (volume-corrected secretin-pancreozym test and glucose-tolbutamide-glucagon provocation, respectively). A close, linear correlation was found between all endocrine variables and pancreatic acinar function (e.g. rs = 0.77 for chymotrypsin output and C-peptide release; p less than 0.0001). The correlation was less strong with pancreatic bicarbonate output (e.g. rs = 0.49 for C-peptide release; p less than 0.05). In our patients, secondary overt diabetes occurred in chronic pancreatitis when protease outputs were, on an average, reduced to about 10% of the mean maximal protease output of normal subjects.