Although initially it was thought that polydimethylsiloxane (silicone) was biologically inert, recent published studies have demonstrated varying levels of IgG antibody reactive with this structure in humans. The objective of our study was to determine whether silicone implanted in humans results in a measurable immune response directed against a 3700 mol wt hydroxyl terminated silicone molecule and whether that response could be correlated with the level of presumed silicone exposure as inferred by clinical history. In a blind study, sera from 111 patients, with and without breast implants, were sent to a laboratory using an enzyme-linked immunosorbent assay to determine specific anti-silicone IgG antibody levels. Test results showed that patients with implants demonstrated statistically significant elevation in anti-silicone antibodies compared with the unimplanted control groups. The highest anti-silicone antibody levels were measured in implanted women with either frank implant ruptures or leakage of their silicone gel implants.