Appropriate rat strains (normal Sprague-Dawley; autoimmune-susceptible Dark Agouti) were used to assess adverse immunological effects of silicone gel and oil. . Four hundred and forty laboratory rats (220 Sprague Dawley, 220 Dark Agouti) were studied. Each rat was labeled using an Electronic Laboratory Animal Monitoring System. To mimic conditions reported in women with breast implants, female rats were inoculated in the mammary area. Prior to the inoculation of the antigens, a control bleed was obtained. The rats were divided into groups of ten. Each group received adjuvant alone or adjuvant emulsified with connective tissue protein. To prepare the emulsion for inoculation, a Polytron Homogenizer was used to emulsify the silicone gel/oil/protein mixture. The emulsion was administered near the right breast of each rat. Serum samples were collected at 2, 5, 8, 12, 24, and 52 wks . The collected samples were centrifuged and stored in a -70°C refrigerator for future ELISA testing. Pathological changes observed were swollen paws, inflamed lymph nodes and thyroid glands, and enlarged spleens. Other pathological changes observed were tumors at inoculation sites and inflamed spleens. Animal tissues were prepared for histopathological analysis between 12 and 24 months following the initial inoculation.