The pharmacokinetic properties of cyclosporine and mainly its absorption and hepatic elimination can vary in each patient in relation to the subject's individual characteristics (inter-subject variability), as well as in an individual patient during his treatment because of clinical episodes or drug interactions (intra-subject variabilities). Therefore, it appears compulsory to follow regularly cyclosporine blood levels or even to characterise each subject following a dose-test during the initiation of treatment, in order to adapt an individual posology aiming to minimise as far as possible the risk of nephrotoxicity.