In order to investigate the effect of lactose concentration and oxygen level on the growth and metabolism of Kluyveromyces Marxiallus UFV-3 in cheese whey permeate, batch cultures were conducted under aerobic, hypoxic, and anoxic conditions, with lactose at initial concentration ranging from 1 to 240 g L-1. The increase in lactose concentration increased ethanol yield and ethanol volumetric productivity, and has reduced cell yield. When lactose concentration was equal or above 50 g L-1 and the oxygen levels were low, the ethanol yield was close to its theoretical value. Maximum ethanol concentrations attained in this study were 76 and 80 g L-1 in hipoxia and anoxia, respectively. The lactose consumption rate in anoxia was greater than in aerobiosis and hipoxia. However, under anoxia, the lactose consumption rate of K. marxianus followed a saturation kinetics, which was not observed in hypoxia and aerobiosis. All oxygen levels investigated, showed a tendency for saturation of the ethanol production rate above 65 g L-1 lactose. Ethanol production rate was also higher on anoxia. (c) 2005 Elsevier Inc. All rights reserved.