The ratio of chymotrypsin to trypsin in the duodenal aspirate was studied in 54 subjects with normal pancreatic function during various stimulation schedules with secretin and cholecystokinin-pancreozymin given by continuous i.v. infusion, and duodenal acidification at a rate of 22 mEq/h. A lowered ratio was observed when cholecystoe kinin-pancreozymin was added to a small background dose of secretin, and when the dose of secretin was increased. These changes correlate with an increase in the rate of secretion of pancreatic juice so that the degree of stimulation appears to influence the ‘dissociation’ of pancreatic enzymes.