The effect of irradiation of the aqueous solution of L. m. muta venom was evaluated with thermic neutrons from Uranium-235 employing doses of 1.61 to 5.19 Gray. The venom was examined for protein content by the Folin Lowry Method modified by Stauffer; for acute toxicity by intraperitoneal route estimation in mice and for immunochemical tests by the antigen-antibody reactions evaluation. Neutronic radiation affects all evaluated parameters in venom (decrease in protein content levels, increase of LD50 values and decrease in the number of precipitating antigen-antibody) as shown by immunodiffusion and immunoelectrophoresis.