A crossover administration of Neoral and Sandimmune was performed in 43 renal allograft recipients who had been on cyclosporine maintenance therapy for 2 to 19 years posttransplant to investigate the pharmacokinetics of cyclosporine. Although there was no difference in C0 values (trough values) when Neoral and Sandimmune were administered at the same doses, AUC(0-4) and AUC(0-12) values of Neoral were 1.57- and 1.36-fold greater than those of Sandimmune, respectively. For both Neoral and Sandimmune, there was a high correlation between the C2 value and AUC(0-4). The Pearson's product-moment coefficient for the correlation between the C2 value and AUC(0-4) was R=0.91642. On the other hand, the correlation with the C0 value (trough value) was low (R=0.53181). During the period of the study, there was no acute rejection episode, onset of adverse drug reaction symptoms, or marked change in laboratory test values.