Antivenin (Crotalidae) Polyvalent, Wyeth, is a refined and concentrated preparation of serum globulins obtained by fractionating blood from healthy horses immunized with the following venoms: Crotalus adamanteus (Eastern diamond rattlesnake), C. atrox (Western diamond rattlesnake), C. durissus terrificus (tropical rattlesnake, Cascabel), and Bothrops atrox ("Fer-de-lance''). Phenol, 0.25%, and thimerosal, 0.005%, are added as preservatives. The product is standardized by its ability to neutralize the lethal action of standard venoms by intravenous injection in mice.1 Dried from the frozen state, the lyophilized serum has a moisture content of less than 1% and is soluble on addition of the diluent contained in each package (Sterile Water for Injection, USP).