1. Lysine deficiency has been produced in rats by placing the weanling animals on an experimental diet in which gluten replaced the casein of the control diet. Both diets were complete in all other known requirements.
2. The resistance of the deficient animals to a subcutaneous challenge of several concentrations of B. anthracis spores, was decreased. Deaths occurred within 2 days post inoculation.
3. When lysine was added to the gluten diet to bring the total concentration to that of the control diet, the growth rate of the animals was maintained but a decrease in resistance remained, although not as great as on the gluten diet.
4. Changes in the tissues associated with lysine deficiency are reported.
5. It is not unreasonable to state that within the time frame of our experiments, the decreased ability of the RES of the host to clear the invading organism from the tissues and subsequently to break down the organism is a major factor of the decreased resistance of the lysine-deficient rats to anthrax.