Pancreatic enzymes and bicarbonate secretion were measured in 95% and 70% pancreatectomized rats by collecting gastric and duodenal juice separately, by means of a chronic gastric fistula, both in the resting state and in response to secretin and cholecystokinin. Two weeks after 95% pancreatectomy, the concentration and the total output of trypsin and amylase were diminished by about 60–80% of the value in the control, whereas bicarbonate and volume remained unaltered. In contrast, during the sixth postoperative week the enzyme secretion normalized itself again in response to CCK. In the 70% pancreatectomized rats, none of the parameters were reduced after 2 weeks. In addition, fecal fat assimilation studies following three different fat diets administered 2 weeks after 95 % pancreatectomy revealed a slight steatorrhea in these animals only after an unphysiologically high fat loading which was completely compensated by addition of pancreatin (10%) to the food. The results are comparable with the clinical experience of subtotal pancreatectomized patients presenting no special problems of maldigestion and suggest that the exocrine pancreas is able to compensate a remarkable large loss of tissue.