Enviromental differences in gentamicin pharmacokinetics by using population pharmacokinetic methods were compared with 20 Korean patients and 24 Korean-American appendicitis patients. Two to six blood specimens were collected from all patients at the following times : just before a regularly scheduled infusion and at 0.5 hour after the end of a 0.5 hour infusion. Nonparametric expected maximum (NPEM) algorithm for population modeling was used. The estimated parameters were the elimination rate constant (K), the slope (KS) of the relationship between K versus creatinine clearance ($C_{cr}$), the apparent volume of distribution (V), the slope (VS) of the relationship between V versus weight, gentamicin clearance (CL) and the slope (CS) of the relationship between CL versus $C_{cr}$ and the V. The output includes two marginal probability density function (PDF), means, medians, modes, variance and CV%. The mean K (KS) were $0.402{pm}0.129;h^{-1}(0.00486{pm}0.00197;[h{cdot}ml/min/1.73;m^2]^{-1})$ and $0.411{pm}0.135;h^{-1}(0.00475{pm}0.00180;[h{cdot}ml/min/1.73;m^2]^{-1})$ for Korean and Korean-American populations, respectively. The mean V (VS) were not different at $14.3{pm}3.6l(0.241{pm}0.0511l/kg)$ and $15.1{pm}3.84l(0.239{pm}0.0492l/kg)$ for Korean and Korean-American populations, respectively (p>0.2). The mean CL (CS) were $5.68{pm}1.69l/h(0.0714{pm}0.0222l/kg[h{cdot}ml/min/1.73;m^2])$ and $5.70{pm}1.77l/h(0.0701{pm}0.0215l/kg[h{cdot}ml/min/1.73;m^2])$ for Korean and Korean-American populations, respectively. There were no enviromental differences in gentamicin pharmacokinetics between Korean and Korean-American appendicitis patients.