Optimal use of cyclosporine microemulsion (CsA ME) in transplant recipients is still a matter of debate. Therapeutic drug monitoring of CsA ME is needed because high variability of inter- and intraindividual exposure to this drug has been reported. Thus, consensus guidelines have been recommended, but the ideal method of follow-up has not yet been found. Pharmacokinetic studies have shown that the 2-hour postdose (C2) sample concentration is more closely correlated with the risk of acute rejection and with toxicity in solid organ recipients compared with the trough (C0) concentration within the first 3 months posttransplantation. For some years, this time point has therefore been used to monitor patients treated with CsA ME. However, there are still some technical (accurate dilution) and practical concerns (education of the patient). Moreover, the target levels of C2, in particular after the first year posttransplantation, are less well defined. Pharmacogenetic studies of the MDR-1 gene as well as the CYP3A4 and CYP3A5 gene polymorphisms could not yet demonstrate any clear influence on the interindividual variations on the pharmacokinetic profile of CsA ME.