yThe permissible region of growth of Saccharomyces cerevisiae on glucose under anaerobic conditions was determined as a function of both pH and the concentration of added acetic acid to the medium. In the absence of acetic acid, growth was possible at a pH as low as 2.5, whereas a total acetic acid addition of 10 gl(-1) increased the minimum allowable pH for growth to 4.5. The results showed that the concentration of the undissociated form of acetic acid should not exceed 5 gl(-1) in the medium for growth to occur. The addition of acetic acid had a profound effect on growth energetics, thereby leading to an increased ethanol yield on glucose. At a concentration of 3.3 gl(-1) of undissociated acetic acid, the ethanol yield was 20% higher than without added acetic acid. Furthermore, the biomass and glycerol yields decreased by 45 and 33%, respectively.