Insulin has proved to be of distinct value in the treatment of patients with diabetes mellitus, but difficulties in the mode of its administration, the danger of overdosage and the transiency of its action have tended to restrict its usefulness. This led to a search for a therapeutic agent which would act like insulin, but which would not possess the latter's disadvantages. As a result, some workers found that untraviolet rays and vitamin Bare capable of producing a distinct improvement in the carbohydrate tolerance of patients with diabetes mellitus. Anderson,1 Rothman,2 Messerle,3 Pincussen4 and Block and Faber5 noted a temporary increase in sugar tolerance as a result of exposing patients to ultraviolet rays. Most of these conclusions were based on depression in blood sugar occurring within three hours after exposure. None of them, however, pursued this study over a sufficiently long period of time to