We have developed an assay to distinguish sapstaining fungi from biocontrol or other fungi present in wood. This assay is based on monoclonal antibody technology. To develop the assay we chose Ophiostoma piceae as the sapstaining fungus and Gliocladium roseum as the biocontrol fungus. We obtained two monoclonal antibodies (Mab) from G. roseum that could be used to discriminate between staining and biocontrol fungi in competition studies. Mab 6A5 could specifically monitor G. roseum and closely related species while Mab 3F12 detected a variety of biocontrol fungi. We had numerous problems in developing a specific monoclonal antibody for O. piceae. We finally succeeded when the cell wall protein from o. piceae was used as an immunogen. One Mab was specific for cell wall protein but could not recognize the whole fungus. This Mab will be used in studies on the cell wall of O. piceae. We developed another Mab that was specific for O. piceae spores and this may be useful in product formulation activities. Three Mabs had high titre and were specific for O. piceae and O. ulmi but did not cross-react with the biocontrol fungi.