Histoplasma capsulatum is an ascomyceteous fungus and a human lung pathogen, which is present in river valleys of the Americas and other continents. H. capsulatum and two related human pathogens, Blasmomyces dermatitidis and Paracoccidioides brasiliensis, belongs to the Ajellomycetaceae family. The genomes of all three species code for three homologous and tentative enzymes of the linoleate diol synthase (LDS) family of fusion enzymes with dioxygenase (DOX) and cytochrome P450 domains. One group aligned closely with 8R-DOX-5,8-LDS of Aspergilli, which oxidizes linoleic acid to 5S,8R-dihydroxylinoleic acid; this group was not further investigated. The second group aligned with 10R-DOX-epoxy alcohol synthase (EAS) of plant pathogens. Expression of this enzyme from B. dermatitidis revealed only 10R-DOX activities, i.e., oxidation of linoleic acid to 10R-hydroperoxy-8E,12Z-octadecadienoic acid. The third group aligned in a separate entity. Expression of these enzymes of H. capsulatum and B. dermatitidis revealed no DOX activities, but both enzymes transformed 13S-hydroperoxy-9Z,11E-octadecadienoic acid efficiently to 12(13S)epoxy-11-hydroperoxy-9Z-octadecenoic acid. Other 13-hydroperoxides of linoleic and α-linolenic acids were transformed with less efficiency and the 9-hydroperoxides of linoleic acid were not transformed. In conclusion, a novel EAS has been found in H. capsulatum and B. dermititidis with 13S-hydroperoxy-9Z,11E-octadecadienoic acid as the likely physiological substrate.