A comparison has been made of the pattern of pancreatic enzyme activities in the duodenal juice of 32 healthy subjects, upon intravenous injection of GIH secretin (1 clinical unit/kg body weight), Farmitalia caerulein (40 ng/kg), or GIH cholecystokinin (1 Ivy dog u/kg), given alone or combined (according to 3 submaximum rapid injection schedules). Enzymatic activities were measured in 5- to 10-min duodenal aspirates. A close correlation between trypsin and chymotrypsin activities was evident under all circumstances. On the other hand there was an apparent delay in amylase and lipase responses after the bolus administration of caerulein or cholecystokinin.