By means of chromatography technique by molecular exclusion using Sephadex G-75 were studied different fractions of venom Crotalus durissus terrificus, one the most common poisonous snakes in Brazil. It were obtained four peaks related to fractions 32, 60, 86 and 103, which molecular weight varied from 4.000 to 150.000. The fractions of all gel filtration diagram were screened through immunoelectrophoresis, in order to verify its charges and migration speed. The precipitation lines were compared with 11 lines obtained through immunoelectrophoresis of total venom against anti-Crotalus durissus terrificus serum. It was observed that fractions of same peak presented peculiar characteristics except fraction 54 (corresponding to the ascending of peak II), which showed significant differences when compared with fraction 60. After screening, fractions of each peak were chosen in order to identify means of double radial diffusion test and the letality was compared with 0,0625 mg/ml concentration of total venom, which corresponds to DL50 in mice by SPEARM & KÄRBER method. Fractions 32, 86 and 103 corresponding to peaks I, III and IV respectively, presented null or negligibe lethality, and fraction II was the most toxic.