Two nematode-parasitic isolates of Harposporium are reported to form synanamorphs attributable to the Hirsutella. One is attributed to Harposporium anguillulae, the second is described as a new species, H. cerberi. H. cerberi also produced an arthroconidial synanamorph. In infection studies of nematodes, conidia typical of Harposporium proved to be capable of killing bacterial feeding nematodes (Rhabditis sp.) when ingested. Infective conidia of H. cerberi were located posterior to the oesophageal bulb, while those of H. anguillulae lodged above it. Hirsutella conidia were not observed to be infective or adhesive, and none of the spore forms was capable of infecting either of two species of stylet-bearing nematodes (Aphelenchus sp. and Meloidogyne hapla).