Crotalus durissus terrificus (South American rattlesnake) venom possesses myotoxic and neurotoxic activities, both of which are also expressed by crotoxin, the principal toxin of this venom. We have investigated the ability of commercial equine antivenom and antivenoms raised in rabbits against C. d. terrificus venom and crotoxin to neutralize the physiological and morphological changes induced by this venom and crotoxin in electrically-stimulated phrenic nerve-diaphragm (PND) and extensor digitorum longus (EDL) preparations of mice. The time required to produce 50% neuromuscular blockade in the PND and EDL preparations was, respectively, 103+/-9 and 59+/-6 min for C. d. terrificus venom (10 microg/ml) and 75+/-9 and 110+/-7 min for crotoxin (10 microg/ml). The antivenoms dose-dependently inhibited this neuromuscular activity of the venom and crotoxin. At a venom:antivenom ratio of 1:3, the rabbit antivenoms were as effective as the commercial equine antivenom. The creatine kinase (CK) concentrations in the organ bath containing EDL muscle were 290 and 1020 U/l following a 120 min exposure to C. d. terrificus venom and crotoxin, respectively. All of the antivenoms neutralized the release of CK by crotoxin, but were ineffective against C. d. terrificus venom. Histological analysis of the two preparations showed that rabbit anticrotoxin antivenom protected against the myotoxic action of C. d. terrificus venom and crotoxin better than the other antivenoms. We conclude that antisera raised in rabbits are better than equine antiserum in neutralizing the neurotoxic and myotoxic activities of C. d. terrificus venom and crotoxin.