Conversion of the main immunosuppressive agent from tacrolimus to cyclosporine (CyA) is a valuable rescue therapy for the severe adverse effects of tacrolimus. We report our experience of the conversion in living donor liver transplantation, in which tacrolimus therapy was converted to CyA. There are few reports describing the optimal initial dose of orally administered CyA (PO CyA) after intravenously administered CyA (IV CyA). We retrospectively investigated the ratio of CyA blood concentrations at 12 hours after the initiation of PO CyA to that just before the conversion, and the ratio of the initial dose of PO CyA to the total dose of IV CyA administered during the 12 hours before the conversion. Linear regression analysis revealed a close correlation between these ratios (y = 2.7 + 5.8x, r = 0.73; P = .002). We recommend that, to maintain a similar trough level of CyA during conversion in liver transplantation, Neoral should be initiated at a ninefold greater dose than the total dose of IV CyA administered during the 12 hours before conversion.