This study was undertaken with the major goal of optimizing the ethanol production from whey using computer technology. To reach this goal, a mathematical model that would describe the fermentation and that could be used for the optimization was developed. Kluyverornyces fmgihs was the microorganism used to ferment the lactose in the whey into ethanol. Preliminary studies showed that K. fragilis produced about 90% of the theoretical ethanol yield when grown in wheycomplemented media. However, when this yeast is grown in nonsupplemented whey media, it does not produce more than 32% of that yield. Comparative batch fermentations of lactose and whey-cornplernented media showed that whey possibly contains enhancing components for yeast growth and ethanol production. To obtain the mathematical model, the one-to-one effect of the process variables (lactose and yeast extract concentrations, air flowrate. pH, and dilution rate) on the ethanol production were first in- vestigated. Experiments on the pH effect showed that a decrease in pH from 7 to 4 produced an increase in ethanoi concentration from 16.5 to 26.5 g/L (50 g/L initial lactose). The results obtained from modeling of the continuous fermentation using the praviously listed variables showed that air flowrate, pH, and dilution rate were the process variables that most influence t h e production of ethanol.