The antigenic properties of alpha-type and beta-type toxins purified from Tityus serrulatus (Ts) venom were analysed by radioimmunoassay, using rabbit antibodies raised against Ts VII, the main beta-type toxin in the venom, and against Ts IV, an alpha-type toxin. The anti-Ts VII serum did not recognize either the other beta-toxins Ts I and Ts II or the alpha-toxin Ts IV; the anti-Ts IV serum did not bind any of the three beta-toxins Ts I, Ts II or Ts VII. Thus, Tityus toxins display at least three distinct antigenic reactivity patterns.