The metabolic fate of silicone gel leaked into the body from an implant is unknown. In this study, serum from 72 women with silicone gel breast implants and 55 control women was blindly assayed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) for elemental silicon. Samples were processed using materials free of silicon. The mean silicon level in controls was 0.13 +/- 0.07 mg/l (range 0.06-0.35 mg/l), while in implant patients, the mean was significantly higher at 0.28 +/- 0.22 mg/l (range 0.06-0.87 mg/l) (P < 0.01, Student's t-test with correction for unequal variances). Using the mean of the control group + 2 SD as a cutoff for normal range (0.27 mg/l), 25/72 (34.7%) implant patients exceeded this value, compared with 2/55 (3.6%) controls. There was no significant correlation between past rupture of one or both implants, current rupture at the time of the blood draw or the number of years with implants and silicon levels. The results suggest that elevations of serum silicon are seen in many women with silicone gel breast implants. The kinetics of this elevation and the actual chemical species of the measured silicon remain to be determined.