Esterase zymograms were obtained following polyacrylamide slab gel electrophoresis of protein extracts Fusarium sambucinum and related species originating from different geographic locations and different matrices. The sites of esterase activity were recorded, and the Rfs were calculated. The data were used for the construction of phenograms by cluster analysis and nonlinear mapping by computerized classification techniques. The fifteen isolates of F. sambucinum, the eight isolates of F. torulosum and the six isolates of F. spec. nov. each had identical profiles, and are therefore electrophoretically distinct species. The isolates of F. sarcochroum, one of F. sambucinum sensu lato (BBA 64280) and fifteen isolates of F. sambucinum were electrophoretically indistinguishable from each other. We assume they are synonymous. The isolate of F. bacteridiodes, one of F. sambucinum sensu lato (BBA 64993) and eight isolates of F. torulosum had uniform EST patterns, therefore the two species are electrophoretically identical. We assume they are also synonymous. The remaining three isolates of F. sambucinum sensu lato are somewhat closely related to F. sambucinum isolates on the basis of our investigations.