Genetic relatedness of 10 strains of opportunistic human pathogenic fungi in the genera Pseudallescheria and Scedosporium and related fungi including Petriella setifera, Graphium tectonae and Ceratocystis fimbriata, were tested by sequencing the entire SSU rDNA. From these molecular data, the imperfect genus Scedosporium can be divided in two, S. prolificans being separable from the S. apiospermum complex. Nearest sexual relatives of S. prolificans seem to be in the microascalean genus Petriella. Strains of Ps. boydii and S. apiospermum, although differing by their previously known DNA/DNA reassociation values, were not separable from each other once a 380 nucleotide long insertion had been removed from the sequence of the two S. apiospermum strains tested. The SSU rDNA of Ps. ellipsoidea is identical to that of Ps. boydii. Fungi which have been known to have Graphium anamorphs can be divided in at least three groups, one of which is related to Petriella and includes Graphium tectonae.