Yeasts had been considered as unable to produce ethanol from pentoses. Ethanol from such sugars is of interest because of the enhancement which would thereby follow in the economics of the bioconversion of lignocellulosics. In one approach to obtain yeasts which convert d-xylose to ethanol screening was carried out. Several were identified and some of the experimental parameters favoring the conversion were investigated. With one of the better converters, Pachysolen tannophilus, ethanol could be obtained from four of the five major phytomass sugars; d-glucose, d-mannose, d-galactose and d-xylose. Using a mutant of P. tannophilus selected for more rapid growth on d-galactose than the wild type, yields from mixtures containing these sugars could be high, in the 83–90% range. Yeasts were also shown to be able to produce ethanol from glycerol and from mixtures of d-cellobiose plus d-xylose, materials whose conversion to ethanol is of potential economic importance. In another approach to obtain suitable yeasts, a gene encoding for d-xylose isomerase in Escherichia coli was cloned. Appropriate introduction of this gene into a suitable yeast host is expected to allow the transformant to convert d-xylose into ethanol.