BACKGROUND: Nephrotoxicity is a frequently encountered adverse effect of calcineurin inhibitors (cyclosporine and tacrolimus)-combined immunosuppressive regimens. METHODS: We have compared the glomerular filtration rate in 14 patients who underwent lung transplantation, before and after replacement of azathioprine by mycophenolate mofetil and reduction of associated calcineurin inhibitors doses. RESULTS: After a mean follow-up of 16+/-4 months with the modified immunosuppressive regimen, the mean glomerular filtration rate increased by 20% with no change in lung function. CONCLUSION: By its strong immunosuppressive effect, mycophenolate mofetil allows the decrease of associated calcineurin inhibitor doses, with subsequent improvement of renal function without jeopardizing the transplanted lung.