The functional reserve capacity of the pancreas, as reflected by the absence of steatorrhea, was correlated with the results of a secretin-pancreozymin test (SPT) in 47 patients with exocrine pancreatic insufficiency due to chronic pancreatitis. The results indicate that a severe reduction in enzyme output (but not in bicarbonate concentration and output) is usually associated with steatorrhea. However, there were a number of patients with steatorrhea despite only moderate enzyme output impairment, while others had normal fat excretion but severely reduced enzyme secretion. Thus, the degree of impaired pancreatic function, as measured by the SPT, cannot be predicted by the presence of steatorrhea; vice versa, a moderately abnormal SPT does not exclude the presence of pancreatic steatorrhea. Therefore, for a sophisticated evaluation of the functional reserve capacity of the exocrine pancreas, both the SPT and fecal fat analysis are considered necessary. The correlation between impaired glucose tolerance and exocrine pancreatic function was poor.