Digestion, enzyme secretion and intestinal rate of passage were determined in broiler chicks from hatch until 21 d using 141Ce as a nonabsorbed reference substance. Body weight and feed intake increased more rapidly after 10 d posthatch, and, in parallel, time of passage of feed through the intestines decreased by approximately 33%. Net duodenal secretion of amylase, trypsin, and lipase was low at 4 d and increased 100-, 50-, and 20-fold, respectively, by 21 d. Enzyme activity decreased distally in the small intestine. This change was greater with age. The contribution of the ileum to fatty acid absorption decreased after 7 d. Small intestine digestion of nitrogen increased from 78% at 4 d to 92% at 21 d, whereas fatty acid and starch digestion ranged from 82 to 89% in this period. It appears that digestibilities of starch and lipids are not limiting factors in the growth of young chicks.