Twenty-one isolates of the nematode-vectored plant pathogen, Dilophospora alopecuri, were examined by allozyme electrophoresis. The study focused on isolates from Australia, including those associated with populations of the seed-gall nematode, Anguina funesta, in Western Australia (W.A.), where the fungus apparently provides natural control of the A. funesta–Clavibacter toxicus association responsible for annual ryegrass toxicity, and a range of Anguina populations in south-eastern Australia. Reference strains from international culture collections were included. Variation was found in 26 of 27 presumptive loci and 10 electrophoretic types were identified. All Australian isolates fell into six electrophoretic types that formed two groups of three that differed by less than 13% within each group, but differed by over 70% between the groups. Of the isolates from W.A., six fell into one electrophoretic type and one into a second electrophoretic type that differed at one locus only. Three exotic isolates varied from Australian ones by 27–74%. Dilophospora alopecuri exhibited greater within-species allelic variation than previously reported for asexually-reproducing halophase fungi. The lack of variation within W.A. suggests that (i) a teleomorph does not occur under local conditions, (ii) the W.A. population has arisen from a single introduction and (iii) selection of strains suitable for biocontrol of Anguina funesta and Clavibacter toxicus should include material from eastern Australia.