ABSTRACTArtificial infection of two grasses and one sedge withAtkinsonella hypoxylonandBalansia cyperi, respectively, is described. Prior inoculations of hosts with these and related fungi in the tribe Balansiae (Clavicipitaceae) have largely been unsuccessful. Seedlings grown in aseptic culture were infected by inserting mycelium and conidia with a needle above the meristem. Infection was evidenced by the presence of mycelium around meristems of new tillers 6–8 weeks after inoculation and by later production of stremata.Atkinsonella hypoxylonstrains from populations of the grassDanthonia spicatawere broadly cross-compatible but could not infect populations ofStipa leucotricha, another host. Strains ofA. hypoxylonfromS. leucotrichacould infect their natural host but notD. spicata.Strains ofB. cyperifromCyperus virensandC. rotunduscould infectC. virensbutA. hypoxyloncould not. The results suggest that there are distinct host races ofA. hypoxylon.Infected seedlings ofD. spicataproduced 50% more tillers than noninfected seedlings after 10 weeks, indicating that this fungus enhances plant growth.