Despite the lack of precise information on the requirements for many of the nutrients essential for cats and dogs and the paucity of information on the availability of nutrients in foods, many commercial diets support excellent growth, reproduction, and maintenance. However, these diets use empirical information that cannot be readily applied to the formulation of new diets. Progress in companion animal nutrition requires more precise information on requirements for various life stages (especially reproduction and maintenance), along with values for the bioavailability of nutrients in dietary ingredients. There is virtually no information on the bioavailability of nutrients for companion animals in many of the common dietary ingredients used in pet foods. These ingredients are generally byproducts of the meat, poultry and fishing industries, with the potential for wide variation in nutrient composition. Claims of nutritional adequacy of pet foods based on the current Association of American Feed Control Official (AAFCO) nutrient allowances ("profiles") do not give assurances of nutritional adequacy and will not until ingredients are analyzed and bioavailability values are incorporated. The AAFCO feeding test provides a superior method for assessing nutritional adequacy to the profile, although the current protocol has procedural and interpretative limitations.