We analyzed the induction of sister chromatid exchange (SCE) by cyclosporin
A (CsA) as a marker of genotoxic potential. In 30 patients undergoing rena
l transplantation, SCE induction was tested before the introduction of CsA
and 3 months later. We found that SCE frequency increased significantly at
the end of 3 months. To our knowledge, this is the first study demonstratin
g in viva induction of SCE by CsA in humans. We conclude that CsA has a gen
otoxic potential on human lymphocytes.