Five different murine monoclonal antibodies (MAbs) to Mycobacterium tuberculosis were examined for degree of cross-reactivity with other mycobacterial species by enzyme-linked immunosorbent assay and immunoblotting. One MAb reacted solely with M. tuberculosis and M. bovis BCG. Two of the MAbs reacted with all mycobacterial species examined, whereas two MAbs demonstrated a limited reactivity pattern. The epitopes are located on molecules susceptible to protease treatment, and two of these molecules possess concanavalin A-binding moieties. Two of the antigens defined by these five MAbs are present in tuberculin purified protein derivative.