AbstractThe utilization and conversion of D‐xylose, D‐xylulose, L‐arabinose, and xylitol by yeast strains have been investigated with the following results: (1) The majority of yeasts tested utilize D‐xylose and produce polyols, ethanol, and organic acids. The type and amount of products formed varies with the yeast strains used. The most commonly detected product is xylitol. (2)The majority of yeasts tested utilize D‐xylulose aerobically and fermentatively to produce ethanol, xylitol, D‐arabitol, and organic acids. The type and amount of products varies depending upon the yeast strains used. (3) Xylitol is a poor carbon and energy source for most yeasts tested. Some yeast strains produce small amounts of ethanol from xylitol. (4) Most yeast strains utilize L‐arabinose, and L‐arabitol is the common product. Small amounts of ethanol are also produced by some yeast strains. (5) Of the four substrates examined, D‐xylulose was the perferred substrate, followed by D‐xylose, L‐arabinose, and xylitol. (6) Mutant yeast strains that exhibit different metabolic product patterns can be induced and isolated from Candida sp. Saccharomyces cerevisiae, and other yeasts. These mutant strains can be used for ethanol production from D‐xylose as well as for the study of metabolic regulation of pentose utilization in yeasts.