The pancreozymin-secretin test was performed on 73 patients with chronic pancreatitis and on 34 with cancer of the pancreas. Duodenal contents were abnormal in 88% of the patients with chronic pancreatitis and in 94% with cancer of the pancreas. The most common abnormality among volume, concentration of bicarbonate, and amylase output of the duodenal contents was low amylase output. The present study strongly suggests that the addition of pancreozymin to the secretin test can detect a diminished enzyme secretory capacity of the pancreas better than can secretin alone. This test can also aid in the diagnosis of diseases of the biliary tract and in differentiating obstructive jaundice by observing changes in bile response of the duodenal contents and by microscopic examination of bile sediment.