Determination of the membrane lipid composition of Saccharomyces cerevisiae revealed an increase in the unsaturation index, qualitative and quantitative changes in sterol content and an alteration of the activity of the plasma membrane ATPase when cells were pre-adapted to ethanol. All these changes may constitute different adaptation mechanisms which allow the cell to cope with ethanol stress. The importance of the lipid environment on the plasma membrane ATPase activity is also discussed.