Intraspecific variability of isoenzymes is described for approximately 20 isolates each of two species of Entomophthora. E. sphaerosperma was found to possess two electrophoretically distinct alleles for phosphoglucoisomerase (PGI), and E. virulenta was found to have three alleles for leucine aminopeptidase, two alleles for 6-phosphogluconate dehydrogenase, and five alleles for PGI. The data suggest that only a single locus codes for PGI in E. sphaerosperma, while two loci code for PGI in E. virulenta. Two strains of E. virulenta isolated in England suggest complete genome duplication. Difficulties inherent in interpreting electrophoretic data from fungi with complicated life histories are discussed.