A mathematic model was developed to simulate the asymmetric reduction of ethyl 4-chloro acetoacetate (ECA) by bakers' yeast. The model of the process considered the kinetics of enzymatic reaction, the effect of substrate inhibition and the spontaneous degradation of the substrate. The reaction kinetics of the ECA degradation was determined empirically. The inhibition by the substrate was analyzed and the apparent kinetic constants of the overall enzymatic reaction, of the S-enzymes and of the R-enzymes, were estimated individually. The system of equations was solved numerically using the Runge-Kutta method. The close correlation between the predicted and experimental results concerning product formation, reaction yield and optical purity of product under various substrate concentrations, implied the reliability of the established model. (c) 2005 Elsevier Inc. All rights reserved.