The fungus Cladosporium fulvum is a biotrophic pathogen of tomato. On susceptible tomato plants, the fungus grows abundantly in the extracellular spaces between the mesophyll cells. The mechanism by which C. fulvum is able to establish and maintain basic compatibility on its one and only host species, the tomato, is unknown. The isolation and characterization of pathogenicity factors and the corresponding genes will provide insight into the mechanism by which C. fulvum colonizes its host. Two putative pathogenicity genes of C. fulvum encoding proteins, which occur abundantly in the extracellular space of infected tomato leaves, were isolated and characterized (ecp1 and ecp2). The DNA sequences of these ecp genes (encoding extracellular protein) do not share homology to any sequence present in the DNA databases. The ecp genes are highly expressed in planta but not in vitro, suggesting that they play a significant role in pathogenesis.