Twenty-eight xylose-utilizing yeast strains were isolated by enrichment culture from 11 samples of feces from the rectum of Murrah buffalo and Swamp buffalo in Thailand. On the basis of their morphological and biochemical characteristics, including sequence analysis of the D1/D2 region of the large-subunit ribosomal RNA gene (LSU rDNA), they were identified as Candida tropicalis (designated as Group I, 11 isolates), Candida parasilosis (Group II, 2 isolates), Candida mengyuniae (Group III, 2 isolates), Sporopachydermia lactativora (Group IV, 2 isolates), Geotrichum sp. (Group V, 5 isolates) and Trichosporon asahii (Group VI, 6 isolates). All isolates utilized xylose as the sole carbon source but 27 isolates could ferment xylose to ethanol (0.006-0.602 g L(-1)) and 21 isolates could ferment xylose to xylitol (0.19-22.84 g L(-1)). Candida tropicalis isolates produced the highest yield of xylitol (74.80%). Their ability to convert xylose to xylitol and ethanol ranged from 15.06 g L(-1) to 22.84 g L(-1) xylitol and 0.110 g L(-1) to 0.602 g L(-1) ethanol, respectively.