The gastrointestinal tract of the newly hatched chick is in a process of development and maturation. In the chicks of domestic fowl and turkeys considerable evidence suggests that, from hatching, the rate of development of the gastrointestinal tract exceeds the rate of body weight gain both physically (relative weight) and morphologically (villus height and perimeter, and villus volume). Rapid development is especially evident in the duodenum, jejunum and pancreas. Once hatched, the time at which maximum specific activities of digestive enzymes has been observed in the pancreas and intestinal brush border vary somewhat, but most often it occurs at or shortly after hatch. Subsequently, specific activities of these enzymes frequently decrease with age. Nevertheless, total digestive enzyme activity tends to increase during the early post-hatch period because of the rapid increase in the weight of the pancreas and intestines. In some instances the increases in total enzyme activity may be too small to keep up with increases in feed intake. For example, a lag in lipase secretion in relation to feed intake may contribute to the relatively poor utilization of some dietary lipids during the first 10 days or so after hatch. Although research findings on digestion and nutrient utilization have varied, there are numerous indications that, in addition to certain lipids, the utilization of some carbohydrates and protein is less efficient during the first week or two after hatch than in older chickens and turkeys. Overall, these observations suggest that additional research is warranted to obtain more definitive information on the development of gastrointestinal function in young poultry.