Silicone [poly(dimethylsiloxane)] gel used in breast implants has been known to migrate through intact silicone elastomer shells, resulting in the clin. observable \"gel bleed\" on the implant surface. Although silicon concns. in capsular tissues of women with silicone prostheses have been measured with element-specific silicon analyses, no silicone-specific investigation of these tissues has been performed as yet. A combination of element-specific inductively coupled plasma high-resoln. isotope diln. mass spectrometry (ICP-HR-IDMS) and species-specific gas chromatog. coupled mass spectrometry (GC-MS) was used to analyze silicon, platinum, and siloxanes in prosthesis capsule, muscle, and fat tissues of women (n=3) who had silicone gel-filled breast implants and in breast tissue of non-augmented women (n=3) as controls. In all tissues of augmented women, siloxanes, in particular octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were identified. Depending on the siloxane species and type of tissue analyzed, siloxane levels in the range of about 10-1,400 ng g-1 were detected; total silicon was found in all tissue samples in the range of about 8,900-85,000 ng g-1. Higher platinum levels ranging from 25-90 ng g-1were detected in fibrin layer and fat tissue of two patients with prostheses. No siloxanes were detected in control breast tissue samples. This investigation of human tissues by a combination of element-specific and species-specific anal. techniques clearly demonstrates for the first time that platinum and siloxanes leak from prostheses and accumulate in their surrounding tissues.