Mycelial proteins from seven isolates of Endothia gyrosa and five isolates of E. parasitica were extracted from acetone powders, separated on polyacrylamide gels by disc electrophoresis, and then stained for general proteins, esterase activity or 3-glucosidase activity. By simple visual inspection, three different observers separated the twelve uncoded general protein gels into the two species. The enzyme gels of both species were more easily differentiated. Very little or no/3-D-glucosidase and general esterase activities were noted on E. parasitica gels. Although the extract sample load (about 220 /xg protein) was standardized, qualitative and quantitative intraspecific variations were noted; these did not interfere with species differentiation. Protein and enzyme profiles from a 30-yr-old isolate of E. gyrosa compared favorably with new isolates. These data corroborate the separation of the species on the basis of morphology.