Soluble culture extracts of Bipolaris australiensis, B. hawaiiensis, B. spicifera, Exserohilum longirostratum, E. mcginnisii, E. rostratum, and Helminthosporium solani were used to prepare reference antisera in New Zealand White rabbits. The absorbed reference antisera were tested by a microimmunodiffusion method against concentrated culture filtrates prepared from 115 environmental and clinical isolates of Alternaria spp., Bipolaris spp., Curvularia spp., Dactylaria sp., Drechslera spp., Embellisia spp., Exserohilum spp., Fusarium sp., Helminthosporium sp., Microsporum sp., Scolecobasidium sp., and Scopulariopsis sp. Cross-reactivity did not occur between isolates of the genera tested except for some Bipolaris and Curvularia spp. Antigens shared by species of Bipolaris and Curvularia correlated with their morphologic similarity and phylogenetic closeness. Cross-reactivity was observed among isolates of B. australiensis, B. hawaiiensis, and B. spicifera and among isolates of E. longirostratum, E. mcginnisii, and E. rostratum. The exoantigen test is valuable for differentiating these fungi at the generic level.