The effect of varying dietary protein content on the activity of human pancreatic proteinases was studied in healthy volunteers. Following the consumption of food with a higher protein content, proteinases activities in duodenal aspirate after pancreozymin and secretin stimulation showed an increasing trend only for a period of 14 days and then returned to their original values. Chymotrypsin is more sensitive and its activity increased significantly. Trypsin activity increased without statistical significance. No evidence of changing other parameter (volume, bicarbonate concentration, amylase and lipase activities) was observed.