Pancreatic protease contents (trypsinogen and chymotrypsinogen) were analyzed in 4- and 8-week-old chickens fed a single 2-hour meal daily. Enzyme activities showed a 24-hour cyclic degression and repletion rhythm. According to the age of the animal, pancreatic depletion preceded (4 weeks) or coincided (8 weeks) with the beginning of the meal. No rhythm was observed in the ad libitum fed chicken. Pancreatic secretion was also studied in the small intestine contents (duodenum, jejunum and ileum, successively) in the 8-week-old chickens.