Some aspects of carbohydrate metabolism in the Wistar albino rat (Rattus norvegicus) and the golden hamster (Mesocricetus auratus) which had been kept in the laboratory at 21° C have been compared. Control blood sugar assays and intravenous glucose tolerance and insulin sensitivity tests were performed. The hamster was shown to have higher fasting and fed blood sugar levels than the rat; it responded equally well to insulin, but showed a comparatively very poor tolerance to exogenous glucose. It is concluded that the hamster maintains a relatively much smaller supply of insulin than the rat.