Five strains of thermotolerant methylotrophic yeasts isolated in Thailand were found to represent three new species in the genera Pichia and Candida, based on phylogenetic analysis of D1/D2 domain of 26S rDNA, in addition to the morphological, physiological, biochemical and chemotaxonomic characterization. Three strains, FS96 and FS101 from flowers and M02 from tree flux, were characterized by ubiquinone Q7, multilateral budding, and the formation of hat-shaped ascospores that are liberated at maturation. These strains showed identical nucleotide sequences in the D1/D2 domain and formed a cluster with Candida thermophila, "Pichia salicis" and Pichia angusta. They differed by 1.9% of nucleotide substitutions from Candida thermophila, the nearest species. They were considered to represent a single new species and are described as Pichia siamensis sp. nov. Two strains, N051 and S023, isolated from soil did not produce ascospores, proliferated by multilateral budding, did not demonstrate urease or DBB color reaction, and lacked sexual stages. These characteristics correspond to the genus Candida. Strains N051 and S023 differed by 2.8% and 1.9% of nucleotide substitutions in the D1/D2 domain from the nearest species, Candida nemodendra and Candida ovalis, respectively, and are considered to represent respective new species. N051 and S023 are described as Candida krabiensis sp. nov. and Candida sithepensis sp. nov., respectively.