APC-conjugated goat anti-rat IgM, µ chain specific, F(ab’)2 fragment antibody reacts with the heavy chain of rat IgM but not with rat IgG. This information on reactivity was based on immunoelectrophoresis and/or ELISA data. This antibody has minimal cross-reaction with human, cow, and horse serum proteins, but it may cross-react with IgM from other species. The antibody was pepsin digested to obtain the F(ab’)2 fragment. Fc fragments and whole IgG molecules have been removed.