Connective tissue disease—like illness has been associated with silicone breast implants. However, no data are currently available on the immunopathology of the capsule surrounding the breast implants. Sera from women with breast implants were collected and assayed for interleukin-6 (IL-6), IL-2, and hyaluronic acid. Capsular biopsies were stained with a probe for HYA or with monoclonal antibodies specific for human macrophages (CD68), T cells (CD4), IL-6, and IL-2. Control specimens consisted of breast biopsies from women undergoing reduction mammoplasty. Our results revealed an increased local amount of hyaluronic acid in the capsule of patients with breast implants compared with control breast tissue. The HYA was localized extracellularly in areas containing fibrosis and cellular infiltrates. The infiltrating cells were determined to be primarily macrophages and T cells. No IL-6 was localized in any of the tissue sections. In contrast, large amounts of IL-2 were found in regions of infiltrating lymphocytes. No significant increase in IL-6, IL-2, or hyaluronic acid was found in the sera. The role of hyaluronic acid and cytokines in the inflammatory response in the capsules of silicone breast implants is discussed.