A continuing program in laboratory animal nutrition involves various stocks and strains of rats, mice and guinea pigs as well as various species of nonhuman primates. A series of factorial designed feeding trials are used to evaluate the effect of diets made from different combinations of ingredients or those varying in nutrient concentrations on the growth, reproduction, maintenance and general health status of the species involved. This program has resulted in the development of open formula natural ingredient diets for various species of small laboratory animals which are currently being used throughout the biomedical research community. An open formula diet is also being developed for nonhuman primates. Data generated by this program are also used as the basis for estimating the nutrient requirements of the various species involved and for ascertaining differences in nutrient requirements for stocks and strains within a species.