ABSTRACTThe similarity of 88 isolates of 27 species ofLeptographiumwas studied using enzyme electrophoresis. UGPMA cluster analysis of similarity matrices (Nei genetic identity, I) generated from data of 267 electrophoretic forms (electromorphs) of 15 enzymes showed a close correspondence between electrophoretic similarity and morphology. Isolates of a species had high similarity and clustered at I≥0.60, and in cases where different taxa clustered at I>0.60, an examination of the morphology and history of the isolates suggested conspecificity. Isozyme characterization was also useful for identifying the extent of morphologic variation within versus between species and for comparing isolates with degenerate morphology after prolonged culture.