Pseudozyma antarctica is one of the best producers of the glycolipid biosurfactants known as mannosylerythritol lipids (MELs), which show not only excellent surface-active properties but also versatile biochemical actions. In order to obtain a variety of producers, all the species of the genus were examined for their production of MELs from soybean oil. Pseudozyma fusiformata, P. parantarctica and P. tsukubaensis were newly identified to be MEL producers. Of the strains tested, P. parantarctica gave the best yield of MELs (30 g L(-1)). The obtained yield corresponded to those of P. antarctica, P. aphidis and P. rugulosa, which are known high-level MEL producers. Interestingly, P. parantarctica and P. fusiformata produced mainly 4-O-[(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl)-beta-d-mannopyranosyl]-meso-erythritol (MEL-A), whereas P. tsukubaensis produced mainly 4-O-[(6'-mono-O-acetyl-2',3'-di-O-alkanoyl)-beta-d-mannopyranosyl]-meso-erythritol (MEL-B). Consequently, six of the nine species clearly produced MELs. Based on the MEL production pattern, the nine species seemed to fall into four groups: the first group produces large amounts of MELs; the second produces both MELs and other biosurfactants; the third mainly produces MEL-B; and the fourth is non-MEL-producing. Thus, MEL production may be an important taxonomic index for the Pseudozyma yeasts.