Isolates of Fusarium oxysporum from different habitats were compared with respect to intra- and extracellular isozymes. Five intracellular enzymes: esterase, superoxide dehydrogenase, malate dehydrogenase, dihydrolipoamide dehydrogenase and succinate dehydrogenase were extracted from the mycelium, and four extracellular enzymes: protease, cellulase (endoglucanase), amylase and lipase were obtained from the culture medium. Proteins were separated either by discontinuous PAGE or by IEF, and isozymes were detected by specific staining. The intracellular enzyme data were analysed by an unweighted paired group method analysis (UPGMA), which separated the isolates into three main clusters. The clusters generated from the intracellular enzymes were weakly correlated with the electrophoretic types based on the extracellular enzymes. These results suggest that extracellular enzymes may be of limited value for classification within F. oxysporum.