On the basis of our previous report that a thymocytotoxic monoclonal autoantibody (NTA260) derived from a New Zealand Black mouse reacts with brain tissues as well as lymphoid cells, the neuronal antigen reacting with this antithymocyte antibody was characterized in the present experiment. Double staining of cultured brain cells with NTA260 and anti-tubulin antibody revealed that both staining patterns closely resembled each other. NTA260 reacted with purified tubulin molecules on Western blotting. Two-dimensional gel electrophoresis of the whole lysate of embryonic mouse brain revealed that NTA260 stained the spot corresponding to that of beta-tubulin but not that of alpha-tubulin. These results suggest that beta-tubulin is a prominent neuronal antigen recognized by NTA260.