The exocrine pancreatic function was studied in humans by performing a secretin-cholecystokinin test before and after treatment with oxytetracycline or chloramphenicol. In the oxytetracycline-treated patients there was a depression of the amylase and lipase outputs in the duodenal secretion, chymotrypsin decreasing only slightly. Administration of chloramphenicol produced a decrease in the amylase output only. After treatment with the two antibiotics the calcium secretion was reduced. The other parameters measured in the duodenal secretion remained essentially unchanged. The enzyme dissociation observed in the present studies is considered to reflect the onset of pancreatic dysfunction due to antibiotic administration. As in the previous animal experiments, the suggested explanation for the changes in enzyme secretion is an inhibition of protein synthesis in the exocrine pancreas due to oxytetracycline and chloramphenicol.