Habu venom and the purified toxic principles (HR1 and HR2) were converted to toxoid with formalin. Immunogenicity was preserved well consistently if formalin was added in several steps to a final concentration of about 0.8%. An adsorbed mixed toxoid composed of purified HR1 and HR2 toxoids was proved to contain all the important antigens necessary for the protection against the envenomation by the Habu bite. Potency of the toxoid preparations can be determined by titrating the circulating antitoxins (anti-HR1 and antiHR2) of the immunized guinea pigs. A practical method for potency test was proposed, in which the potency is expressed in the relative value to a reference toxoid.
