Pharmacokinetic studies were performed in 10 Thai patients with kidney transplantation who received microemulsion formulation (Neoral) of cyclosporin A (CsA) twice daily. No agents having pharmacokinetic effect on CsA had been used in these patients. The mean values of 12-h AUC (area under the concentration-blood curve) were 4603.63 +/- 344.61 ng x h/ml. CsA concentrations at 2 hours after dosing had the best value of correlation coefficient with the 12-h AUC. Abbreviated AUC could be calculated by stepwise multiple linear regression analysis and linear trapezoidal rule. The latter is more simple and superior to the former one.