Two lots of purified protein derivative of tuberculin with different potencies determined by skin tests on guinea pigs, were examined for their capacity to induce shock in hamsters sensitized with BCG. Groups of hamsters were injected with varying doses of a highly potent strain of BCG grown in Dubos fluid medium. 4–5 weeks later two groups of animals sensitized with corresponding doses were injected intraperitoneally with 1 mg of each lot of tuberculin. 12 of the 20 hamsters given the strong tuberculin died, while all those given the weak tuberculin survived. An attempt was made to evaluate the mutual potency of the two lots of tuberculin by injecting groups of sensitized animals with 1 mg strong or 4 mg weak tuberculin. The difference in the number of deaths from shock in the two groups was not significan