The objective of this matched case-control study was to determine whether women with Même or Replicon polyurethane-covered silicone breast implants are exposed to clinically significant levels of free 2,4-TDA from biodegradation of the polyurethane foam. Urine and serum samples were obtained from 61 patients with Même or Replicon breast implants and 61 controls on two separate occasions separated by 10 +/- 3 days. Free TDA was analyzed by gas chromatography combined with negative chemical ionization mass spectrometry with lower limit of quantitation in both urine and serum of 10 pg/ml. The results were correlated with the length of time since implantation. No patients or controls had detectable free 2,4-TDA in their sera. Thirty patients had quantifiable levels of free 2,4-TDA, and 18 had detectable levels in their urine. Controls had no quantifiable levels, but 7 subjects had detectable levels. The biodegradative half-life of the polyurethane foam was estimated to be 2 years. A risk assessment using the cancer potency estimate calculated by the FDA from rat data and the National Academy of Sciences methodology provided a theoretical lifetime risk of approximately one in one million. It was concluded that the polyurethane foam cover on the Même and Replicon breast implants biodegrades. The risk assessment of approximately one in one million derived from this study strengthens earlier conclusions by the Health Protection Branch (Canada) that there is no significant risk of cancer from exposure to the 2,4-TDA formed from this biodegradation.