Hyalohyphomycoses caused by Pseudallescheria boydii and Scedosporium apiospermum have recently been on the increase. To find the appropriate treatment for this emerging disease, we examined the antifungal susceptibility of 10 isolates of P. boydii and 17 isolates of S. apiospermum, most of which were isolated from clinical specimens. When the NCCLS M38-P microdilution method was used, itraconazole showed strong antifungal activities, while amphotericin B had little efficacy. A new triazole agent, voriconazole showed a strong effect against isolates of P. boydii and S. apiospermum (MIC50 0.06 micro g/ml), whereas micafungin, a newly developed echinocandin, had little effect (MIC50 >16 micro g/ml). There was no significant difference in the susceptibilities between P. boydii and S. apiospermum isolates against any antifungal agents. Our study suggests that voriconazole is a promising new drug in these infections, and that the same antifungal strategy can be employed in the infections by P. boydii and S. apiospermum.