Silicone can cause neuroimmunologic disorders with a variety of symptoms, probably due to global activation of the immune system. Immunological evaluations were conducted on the blood samples of two hundred symptomatic patients with silicone breast implants and compared with one hundred symptomatic patients with chronic fatigue and one hundred normal controls. These tests were classified under three different categories: A. A. Neurologic antibodies, which included myelin-associated glycoprotein, ganglioside GM1, and sulfatide IgG, IgM, and IgA antibodies. These antibodies were found to be elevated in up to 69.5% of the silicone patients while 37% of the group with chronic fatigue had elevated levels of these antibodies, as did 12% of the normal controls. B. Immune functional abnormalities, which included T-helper/suppressor ratio, percent B-cell, lymphocyte immune function testing, and NK cytotoxic activity. T-helper/suppressor ratios were elevated in 37-38.5% of both symptomatic groups, compared to only 8% of controls. All other immunological testings were statistically significantly higher in the silicone group than in the chronic fatigue group or control group. C. Tests for connective tissue disease, which consisted of rheumatoid factor, C1Q immune complexes, C3, C4 complement, ANA, thyroid antibodies, and phospholipid antibodies. Similar to the studies of neurologic antibodies and immune function, these tests were very abnormal in the silicone implant group, when compared to controls or even to the symptomatic group without silicone. The results of this study indicate once more the need for proper laboratory testing for the diagnosis of atypical neurologic and connective tissue diseases exhibited in symptomatic patients with silicone breast implants.