Comparative vaccination studies were made between a strain of live BCG and an ultraviolet-killed strain of virulent human tubercle bacilli. Guinea pigs were used as test animals. Three doses of the irradiated vaccine produced as effective resistance against a challenge dose of virulent organisms as one dose of live BCG. The irradiated vaccine was more effective than a heat-killed vaccine prepd. from the same virulent strain and also more effective than irradiated BCG. Evaluation of the vaccines was made on the basis of survival times over those of control animals. No vaccine gave complete protection against the virulent challenge strain.