Cyclosporine (CsA) is a major immunosuppressive drug used widely to prevent organ allograft rejection. fits potential organotoxicity by prolonged use is known to cause both direct tissue damage and indirect pharmacokinetic interactions with other drugs. This study was performed to determine the effect of nicardipine (NCP) on the pharmacokinetic parameters of CsA in Sprague-Dawley rats. Each rat was administered with CsA in saline-treated group or in NCP-treated group which was pretreated with NCP (5 mg/kg/12 hours, i.p.) for 6 days. The plasma CsA concentration were analyzed by reversed HPLC: UV system at 0.5, 1, 2, 4, 6, and 8 hours after bolus injection of CsA (10 mg/kg). Pharmacokinetic parameters (mean$pm$ SD, n=7) such as initial plasma concentration (C(0)), mean residence time (MRT), steady-state volume of distribution (Vdss), terminal half-life (t$frac{1}{2}$($eta$)) and plasma clearance (CLp) of CsA in each groups (saline-group vs NCP-group) were determined as follows: C(0) (5.66$pm$ 1.98 vs 17.98$pm$2.36, p<0.01); Vdss (2.68$pm$ 1.6 vs 0.94 $pm$ 0.25, p<0.01); CLp (0.53 $pm$0.18 vs 0.21 $pm$0.06, p<0.01). Therefore, Our results indicate that nicardipine significantly affects the pharmacokinetic parameters of cyclosporme, especially C(0), Vdss, and CLp in NCP-treated group. We suggest that the significant pharmacokinetic interaction between cyclosporine and nicardipine should be considered and cyclosporine level should be closely monitored and dosage reduction made as necessary in clinical situation that was coadministered with CsA and NCP.