Abstract : Data are presented to support the hypothesis that animals resistant to the establishment of anthrax are susceptible to its toxin, the former shown by dose of organisms and the latter by challenge with sterile toxin, and by the number of organisms and units of toxin per ml in terminal blood. The variables discussed are dose, doubling rate in the blood, terminal number of organisms per ml of blood, units of toxin per ml of terminal blood, inhibition of phagocytosis by toxin, spore germination within the phagocyte, quantitative phagocytosis in vitro, and lysis of phagocytes in vitro. The need for quantitative information from field cases of anthrax is emphasized for its usefulness as research information per se and to more completely understand field anthrax. In addition, the information obtainable by a field serological survey and its use are discussed.