During experiments designed to determine the effect of insulin on local and systemic delayed-type hypersensitivity reactions in the rat (1,2,3) an unexpected effect of insulin, or insulin and Old Tuberculin in combination, was encountered in the fall of the year. The reactions seen were apparently due to a seasonal variation in behavior and metabolism, a very common problem 'found by those working with rats and mice, which can occur in either the spring or fall. The following is a description of the initial experiments in which the presence of a syndrome, since proven to be related to sulfur deficiency, was established.