The effects of long-term hyperstimulation with cholecystokinin (CCK) on the pancreatic contents of anionic and cationic trypsin(ogen) and amylase were studied in the rat. Endogenous hyperCCKemia was evoked in rats by pancreaticobiliary diversion (PBD), and exogenous hyperCCKemia by continuous subcutaneous CCK infusion. In addition, the effect of continuous subcutaneous infusion of the CCK A receptor antagonist devazepide was studied. After 4 weeks blood samples were obtained for the determination of plasma CCK concentrations and the animals were sacrificed. The pancreatic glands were harvested, weighted, and extracted. The extracts were analyzed for anionic and cationic trypsin and amylase. Enzyme contents showed a large interindividual variation. The most consistent change in enzyme pattern was an increase in the ratio between anionic and cationic trypsin in animals with hyperCCKemia (PBD operated or CCK infused). Furthermore, this ratio decreased significantly in animals treated with devazepide. In conclusion, stimulation of the CCK receptor changed the ratio between anionic and cationic trypsin in the pancreatic gland, while it was reversed during blockade of the receptor.