Nutritionally physiological patterns of Pseudallescheria boydii (Microascaceae) and the related species Scedosporium prolificans were established. Differences between the two species were found in assimilation of sucrose, ribitol, xylitol and L-arabinitol. In contrast, no physiological distinction could be made between the three intraspecific variants of P. boydii which have been recognized on the basis of nDNA/DNA homology data and of morphological and clinical differences. Some potential virulence factors were studied in the fungi mentioned above and in some related anamorphs. All species were capable of anaerobic growth, but differed in their temperature relations.