The time-course accumulation patterns of ß1,3-glucanase and chitinase isoforms in susceptible tomato roots inoculated with either pathogenic or non-pathogenic strains of Fusarium oxysporum were investigated with regard to the fungal dynamics of root colonization. Eleven days after inoculation, isoelectric focusing gel electrophoresis showed an overall increased activity of constitutive glycosidase isoforms in response to infection by F. oxysporum f. sp. lycopersici that did not occur in roots colonized with non-pathogenic strains. As detected by anodic polyacrylamide gel electrophoresis for acidic proteins, the strains of F. oxysporum f. sp. lycopersici induced the expression of at least one additional ß-1,3-glucanase. This isoform, supposedly of host origin, may serve as a biochemical marker of pathogenicity in fusarium wilt of tomato. The present study does not seem to support the view that the postinfectional accumulation of chitinases and ß-1,3-glucanases might play a significant role in restricting the root colonization by pathogenic strains of F. oxysporum.