Cheese whey powder (CWP) solution was used for ethanol fermentation by Kluyveromyces marxianus NRRL-1195 in batch experiments. Effects of initial pH. CWP concentration and external nutrient (N, P) supplementation on ethanol formation rate and extent were investigated. The initial pH was varied between 3 and 7. The most suitable initial pH maximizing the final ethanol yield was found to be 5. Nutritional requirements of the organisms were investigated by supplementing the CWP solution with external nitrogen and phosphate sources. The rate and extent of ethanol formation did not increase with external nutrient addition indicating the fact that the nitrogen and phosphorous content of CWP was sufficient for ethanol fermentation. CWP concentration was varied between 50 and 300 g l(-1) with total sugar concentrations between 25 and 150 g l(-1). Final ethanol concentration and the rate of ethanol formation increased with increasing CWP concentration indicating no substrate or product inhibitions, but substrate limitations. The yield coefficient of ethanol varied between 0.35 and 0.54 g ethanol g sugar I and reached the theoretical level (0.54 a EtOH a sugar(-1)) at 300 g l(-1) CWP concentration. (c) 2005 Elsevier Inc. All rights reserved.