The clinical efficacy of calcineurin inhibitors administered to renal transplant recipients is considered to be a strong function of the area under the concentration time curve (AUC). Monitoring of blood concentrations for two similar calcineurin inhibitors, cyclosporine (CyA) and tacrolimus (TAC) are different. Namely, CyA blood concentration is usually monitored at two hours after administration (C2), a surrogate for peak concentration (Cp), and TAC at trough concentration (Ct). We examined the behavior of blood concentration curves simultaneously for both CyA and TAC in renal transplant recipients with similar clinical backgrounds. Furthermore, we analyzed the correlation of Cp and Ct vs AUC implementing an area under the trough level, or area above the trough level as new pharmacokinetic parameters, so that C2 for CyA and Ct for TAC has validated using controlled clinical data. We observed differences in the pharmacokinetics between.