A kinetic model for continuous fermentation of ethanol from cheese whey was developed. The model accounts for substrate limitation, substrate inhibition, ethanol inhibition and cell death. Three bioreactors of 5 L volume each were operated at different hydraulic retention times (HRT) ranging from 18 to 42 h and initial lactose concentrations ranging from 50 to 150 g/L. The experimental data were used to validate the model. The model predicted the cell, lactose and ethanol concentrations with high accuracy (R' = 0.96-0.99). The cell concentration, lactose utilization and ethanol production were significantly affected by hydraulic retention time and initial substrate concentration. Lactose utilizations of 98, 91 and 83% were obtained with 50, 100 and 150 g/L initial lactose concentrations at 42 h HRT. The highest cell concentration (5.5 g/L), highest ethanol concentration (58.0 g/L) and maximum ethanol yield (99.6% of theoretical) were achieved at 42 h HRT and 150 g/L initial lactose concentration. (C) 1997 Published by Elsevier Science Ltd.