This is an extension of an earlier study in which we found that while commercial "enriched" bread alone would not support the life of weanling rats in a 90-day test, enrichment could be updated at low cost, with the result that rats consuming the improved bread alone lived during the test period and grew seven times as fast. Prominent nutritionists criticized this study on the basis that bread is not eaten alone and that other single foods are likewise deficient. It was stated: "the experiments you performed would have given the same or similar results if you had begun with milk, eggs, meat, or any other food". Skepticism regarding this statement led to experimental trials in which milk, meat, eggs, and several other foods, including breakfast cereals, were fed singly to groups of animals. Eggs proved to be a remarkably complete food, and milk exhibited about the same excellence until the iron deficiency became evident after about two months. "Enriched" breakfast foods and macaroni were highly deficient and could be improved greatly by supplementation.As an outgrowth of this study, we are developing a method of biological testing which is incomparably better for evaluating foods than consulting food composition tables. On the basis of the tabulated data alone one might conclude that "enriched" puffed rice, for example, is only slightly inferior nutritionally to eggs. Our experiments have shown this assumption to be grossly in error.