The murine antibody response to porcine insulin is controlled by immune response genes of the major histocompatibility complex. Animals of the one haplotype (H-2(d)) produce specific antibodies to pork insulin, while animals of other haplotypes do not. We analysed the antibody responses to purified pork insulin by animals of responder and non-responder haplotypes, and attempted to correlate these responses with histopathological findings at necropsy. Animals of responder and non-responder haplotypes immunized with insulin or control preparations generally presented similar pathological pictures. We found granulomatous inflammatory infiltrates in the liver and the periphery of the pancreas, mononuclear interstitial pancreatic infiltrates, and mononuclear hepatic pericholangitis. Those we ascribe to adjuvant. One animal (H-2(d)) immunized with insulin showed focal peri-insulitis. Otherwise, the inflammatory infiltrates in the islets reported by others were not observed. The significance of insulitis in experimental insulin immunity is discussed.