A monoclonal Listeria antibody, designated B4, was evaluated. The ability of the antibody to bind to viable bacteria belonging to Listeria spp. compared to bacteria of the same species killed by heat treatment, acid or base treatment, sanitizers, and irradiation was examined. The antibody was found to react with viable L. monocytogenes and L. innocua, but not with heat-killed (72 degrees C, 5 min) strains of these organisms. When L. monocytogenes and L. innocua were killed by methods other than heat treatment, it was ambiguous whether the antibody detected the organism or not. It was concluded that the B4 antibody has potential to be used in an immuno capture step to capture live L. monocytogenes and L. innocua from foods prior to identification of L. monocytogenes by polymerase chain reaction (PCR).