Human lymphocytes cultured in vitro were used to assess the ability of polymethyl methacrylate (PMMA), currently used in orthopedic surgery as bone cement, to induce sister-chromatid exchanges (SCE). Under the conditions used in this study, PMMA bone cement did not produce any significant increase in SCEs in phytohemagglutinin-stimulated human lymphocytes. However, a significant decline (p less than 0.05) in the proliferation rate index was observed, which might be an indicator of the cytotoxic effect of PMMA.