Mycobacterium bovis strain BCG, substrain 1173P2, has been grown in homogeneous culture in classical synthetic Sauton medium without supplementary ingredients. The culture conditions are described. The protein release in the culture medium and the tuberculin yield after 2% trichloroacetic acid precipitation were significantly improved. The antigenicity of the tuberculin has been successfully assayed on specifically sensitized guinea-pigs. It is concluded that homogeneous mycobacterium culture in a fermentor using synthetic medium is a suitable method for the large scale production of antigen.