Duodenal, jejunal, ileal and caecal morphometries were determined in chickens from hatching to the age of 15 weeks. The ratios of fresh weight/surface area and dry weight/surface area showed age- dependent changes in all the intestinal segments studied. The percentage of mucosa in each segment was also age-dependent in the first three weeks of life with a higher participation in the proximal intestine. Transport of 3-oxy-methyl-D-glucose was determined in the jejunum and ileum using a perfusion technique in vivo and expressed as a function of fresh weight, dry weight and surface area. The age- dependent differences observed in weight and mucosa composition of the intestine make it difficult to interpret the results of transport capacity during development. The optimum expression of results in the field of intestinal absorption may be the surface area, since it involves the smallest errors.