Fiock, Mary A. (Fort Detrick, Frederick, Md.), Allen Yarinsky, and James T. Duff. Studies on immunity to toxins of Clostridium botulinum. VII. Purification and detoxification of trypsin-activated type E toxin. J. Bacteriol. 82:66-71. 1961.-A procedure was described for production, purification, and conversion to toxoid of the Clostridium botulinum type E trypsin-treated toxin. A medium containing 1.5% trypticase, 0.5% yeast extract, 0.075% cysteine hydrochloride, and 1.0% glucose consistently yielded activated culture toxicities of 300,000 mouse intraperitoneal ld(50)/ml. Purification of the toxin was accomplished by precipitation with ammonium sulfate, extraction with calcium chloride, and reprecipitation with ethanol in the cold. The resulting partially purified toxin had a specific activity of 45,000,000 ld(50)/mg nitrogen. Purified toxins were converted to toxoid by incubation with formalin and adsorbed on aluminum phosphate. Good immune responses were obtained to the toxoids in mice, guinea pigs, and rabbits.