Fibrous tissue capsules, from around silicone breast implants, were examined by light microscopy, and by transmission and scanning electron microscopy, the latter combined with energy dispersive X-ray analysis. Contractile fibroblasts (myofibroblasts) were found in most of these fibrous capsules, and especially in those recently formed or manipulated. The element silicon was positively identified by X-ray analysis in half the tissue specimens. This material was found only around gel-filled implants. In the specimens studied, the clinical hardness of the breast was unrelated to the presence of silicon in the capsule.