From unfimbriated Escherichia coli O20:KX104: H−, which caused systemic infection in man, and adhesin (NFA-3) was isolated by extraction from the bacteria in phosphate buffered saline at 70°C. It was purified by ammonium sulfate precipitation and anion exchange chromatography in the presence of urea. The adhesin had an apparent molecular weight in excess to 106 daltons and consisted of 17.500-d peptide subunits. It had an isoelectric point of 3.9 and contained one cysteine and no methionine. In haemagglutination assays and adhesion immunoassays, NFA-3 showed a preferred specificity for blood group N.