We determined the ability of a mixture of gangliosides (16% GD1b, 19% GT1b, 21% GM1, 40% GD1a) to neutralize the effect of Crotalus durissus terrificus (Cdt) venom in vitro and in vivo. Protection was indicated by the absence of muscular contractions, hind limb paralysis or death of BALB/c mice (16-18 g) after receiving Cdt venom (1 microgram Cdt venom containing 0.6 microgram protein) at the doses indicated. A dose of Cdt venom above 0.9 microgram (ip) or 1 microgram (im) induced muscular contraction and above 1.2 micrograms (ip) or 5.5 micrograms (im) the venom induced muscular contraction and hind limb paralysis. Cdt venom above 2.5 micrograms (ip) or 9 micrograms (im) induced all these symptoms and 95 to 100% death in experimental animals. The lethal dose 50% of the Cdt venom used was 8 micrograms (im) and 1.5 micrograms (ip). In in vitro studies, 4 mg gangliosides neutralized the effect of up to 1.5 micrograms Cdt venom. Quantities as low as 0.2 mg gangliosides were capable of neutralizing 0.9 microgram of Cdt venom in vitro. Intramuscular treatment with 1 mg gangliosides performed 60 min after the intramuscular injection of 5 micrograms Cdt venom protected 100% of the animals. In contrast, no protection was achieved with intraperitoneal treatment with gangliosides. The data show that gangliosides were effective in neutralizing the toxic effects induced by Crotalus durissus terrificus venom both in vitro and in vivo and that post-exposure intramuscular treatment with gangliosides could protect animals experimentally inoculated with the venom.