Concern has been raised that collagen, a connective tissue protein, may be involved in autoimmune diseases reported in women with gel-filled breast implants. It has been suggested that silicone gel may act as an adjuvant to mediate the immune responses to host connective tissue proteins associated with breast implants. As part of our studies of this problem, we are using normal rats (Sprague-Dawley) and rats genetically susceptible to autoimmune disease (Dark Agouti) immunized with silicone as adjuvant plus collagen as antigen. In addition to the production of collagen antibodies, analyses of animals during necropsy demonstrate immunopathological changes caused by silicone gel and oil. Results reveal that silicone gel can migrate to distant anatomical sites or remain at the implantation site for at least one year. Spectroscopic studies were used to detect the presence of newly formed collagen at sites distal to the injection site but associated with migrated silicone gel. Elevated serum levels of tumor necrosis factor were detected in the silicone-treated normal rat strain but not in the serum of autoimmune-susceptible rats. Migration of silicone and cellular localization of oil and gel are similar to effects observed in some women with breast implants. These animal models are useful for studying potential adverse immunological effects of biomaterials, including silicone.