We collected pure pancreatic juice during an entire day and examined pancreatic secretory changes induced by ordinary meals in a male patient having an external drainage of the main pancreatic duct. The ingestion of breakfast, lunch, and dinner each caused a marked increase in pancreatic secretion above basal levels. The increase in both bicarbonate and protein output was very prolonged. The highest secretory outputs induced by meals were slightly higher than those produced by exogenous administration of submaximal doses of secretin and cerulein. The profile and magnitude of bicarbonate and protein secretion were similar.