A panel of monoclonal antibodies (MAbs) was raised to Botrytis cinerea using four different immunogens. Co-immunization with cross-reactive monoclonal antibodies helped to increase the percentage of specific hybridoma cell lines produced. The abilities of the MAbs to detect fungal antigens in extracts from infected tissue was correlated with their taxonomic specificities and with the localization of the antigens on the surfaces of the hyphae and conidia. Four distinct groups were identified: taxonomically unrelated, near-genus-, genus- and near-isolate-specific. Genus-specific antibodies gave the highest absorbance values in ELISAs with extracts from infected plant tissues. MAbs from this group all recognized heat-stable epitopes on antigens expressed along the length of the extracellular matrix of the hyphae and surface of the conidia. Antibodies from this group were all IgG1 antibodies.