A monoclonal lgG 1 antibody against F8 fimbriae was obtained with the hybridoma technique using spieen cells from C3H/f rnice immunised with a fimbrial preparation of Escherichia coli 2980 (018ac: K5: H-: FIC, F8) and Sp 2/0 Ag8 myeloma cells. The hybrid cells were cloned twice by lirniting dilution and grown in tissue culture. The monoclonal antibody was purified from culture supernatants on Protein A Sepharose. lt reacted with F8 fimbriae in colony blot, enzyme-linked immunosorbent assay (ELISA) and immunoblot after electrotransfer from sodium dodecyl sulphate-polyacrylarnide gel electrophoresis (SOS-PAGE) of fimbrial preparations. The antibody bound to and agglutinated F8-fimbriated bacteria.