In the phylogenetic tree based on D1/D2 26S rDNA sequences, the three strains were located at the same position and clustered with Candida thermophila, “Pichia salicis” and Pichia angusta (Fig. 1). The strains had identical nucleotide sequences and differed from Candida thermophila, the nearest taxon, by 1.9% sub- stitutions (11 of 566 nucleotides). According to Kurtz- man and Robnett (1998), yeast strains showing that nucleotide substitutions greater than 1% in this domain (ca. 600 nucleotides) are likely to be different species. We therefore treat the three strains as a new species of the genus Pichia. The name Pichia siamensis is given for these strains.