Experimental ciclosporin (CSA) nephrotoxicity is reported to be more severe in male versus female rodents. To investigate these sex differences further, groups of male and female Sprague-Dawley rats were pair fed and given either CSA 50 mg/kg or olive oil vehicle by gavage daily for 5 days. Both groups of treated animals showed azotemia and depression of CIn but there were no sex differences. CSA levels were 5,820 ng/ml in females and 6,480 ng/ml in males (p = NS). Although CSA did not produce enzymuria in either sex, females showed more extensive proximal tubular cell vacuolization. CONCLUSIONS Female Sprague-Dawley rats are equally as susceptible to CSA nephrotoxicity as males. Strain differences or experimental design may account for apparently conflicting results in the literature.