From a culture of Escherichia coli, strain B44, pili K99 was purified and used for generating murine monoclon al antibodies. These IgG1 antibodies, purified from ascitis by immunoaffinity Protein G-Sepharose chromatography, maintained their biological activity in immunoradiometric assays. Since enterotoxigenic E. coli is one of the main agents of neonatal bovine diarrhoea, it is biotechnologically important to generate monoclonal antibodies that recognize one of the main adherence factors, pili K99. Thus, these antibodies offer an interesting possibility to detect the bacteria in biological fluids and to attempt the immunoaffinity purification of the adherence factor.02FONDEF002FONDEF628