Sertaconazole is a new synthetic antifungal which has shown promising activity against numerous fungi. The morphological changes induced by the drug at two concentrations, the MIC and 10 times the MIC, during 24 and 48 h on the filamentous opportunistic fungi Aspergillus fumigatus, Chaetomium atrobrunneum and Scedosporium prolificans indicated that the intensity of the ultrastructural breakdown depended on the dose and not on the time of exposure. Common severe alterations of many fungal cells, which could be considered beyond repair, were seen at the cell wall, plasmalemma and cytoplasm levels. The results obtained underline the drug efficacy for those fungi and suggest its applicability as therapeutic agent in the human infections produced by them.