Cyclosporin A (CSA) is a new, potent immunosuppressive agent which is of proven value in organ transplantation. The use of CSA is associated with numerous side-effects, of which a dose-dependent nephrotoxicity is the most serious. CSA nephrotoxicity can be divided into two major groups: (i) functional toxicity without significant morphological lesions and (ii) morphological forms of toxicity with tubular and/or vascular-interstitial lesions. Vascular-interstitial toxicity is the most serious form because the renal lesions are irreversible.