The localization of insulin I125 in oral tissues of the rat was investigated. Eight rats were made chemically diabetic in order to study the tissue distribution of insulin I125. Two nondiabetic control animals were also injected with the tracer. Another animal served as a complete control (i.e., not injected with either the diabetic inducer or insulin I125). Additional controls were sections of thyroid and liver. Experimental rats were sacrificed at preselected time intervals and autoradiographic procedures were performed subsequent to conventional histologic studies. Qualitative grain counts were made of each slide in order to compare with the background count. All oral tissues studied except dentin showed insulin I125 uptake.