Direct microcytotoxicity testing and absorption analyses were employed to determine whether H-2K, H-2D, and Ia antigens are present on murine islet of Langerhans cells. Products of the H-2K and H-2D loci were found on beta-cells from three different mouse strains, but I-region (Ia) antigens were not detected. The absence of Ia gene products from islet cells may be of importance in explaining the survival of islet allografts across major histocompatibility barriers.