Background: To test the bioequivalence, the bioavailability of the newly marketed cyclosporine microemulsion preparation NEOPLANTA(Hanmi Pharm. Co., Ltd, Seoul, Korea) was compared with SANDIMMUNE NEORAL(Sandoz Pharm. Co., Basel, Swiss) as a reference drug. Method: Twenty four normal volunteers were entered to the study(Yonsei University College of Medicine, Severance Hospital IRB approval No.9606). They were administered 175mg of cyclosporine in $2;{ imes};2$ crossover design with two weeks of drug free period between doses. The blood sampling was done before and after administration upto 24hours. The concentration of cyclosporine was measured by radioimmunoassay. A non-compartmental method was applied for analysis of the concentration-time data. Results: The area under the curve(AUC), maximal concentration of drug(Cmax) and time to reach Cmax(Tmax) did not show any significant difference between two preparations by ANOVA. The mean differences of AUC, Cmax and Tmax were within 20% of the reference drug, those were 8.31%, 2.58% and -4.73%, respectively. The confidence limits of three parameters were satisfied the bioequivalence criteria. Conclusion: These results suggest that the test cyclosporine microemulsion preparation NEOPLANTA is bioequivalent to the reference drug.