A filtration flow-through design was used to develop the rapid immunodetection of Escherichia coli. Polyclonal anti-E. coli IgG was conjugated to small, 0.8 mu Blue latex beads. Cells were mixed with conjugated beads in the presence of anti-E. coli monoclonal IgM. The suspension was then filtered through a 5 mu nitrocellulose membrane. The cell-containing complexes were effectively collected on the filter, forming a blue spot. The method produced reliable detection of E. coli at a concentration of 10(5) cells ml(-1), which is a current benchmark figure for urinary tract infection (UTI) diagnosis.