A kinetic analysis of Kluyveromyces lactis fermentation on whey is reported. Batch and fed-batch operations have been considered in 10, 100 and 1000 1 fermenters. A simple kinetic model for cell growth during batch and fed-batch operation was used. As expected, the specific growth rate was well represented by the Monod equation. Parameters have been estimated by fitting the model to experimental results achieved in the batch step. Results obtained in the fed-batch operation showed the ability of the model to predict K. lactis fermentation courses on whey in different scales. (C) 2001 Elsevier Science Ltd. All rights reserved.