Pachysolen tannophilus is a yeast capable of fermenting xylose to ethanol. This organism is of interest due to its potential for converting the xylose found in agricultural and forestry residues to ethanol. From this study, it has been determined that when Pachysolen tannophilus is grown on xylose at 37/sup 0/C, xylose reductase activity is greatly reduced from that found in cells grown on xylose at 30/sup 0/C. Even though xylose reductase activity is reduced, cellular growth and division continues to occur at the higher temperature, suggesting either that xylose reductase activity is not a rate-limiting step in the utilization of xylose or that there is an alternate pathway for xylose utilization in Pachysolen.