Sera of patients, blood donors and cattle sera were examined by means of diffusion--in--gel technique using self produced antigens, prepared from H 37 Ra, one fresh isolated strain of M. tbc and BCG Jena. 38.2% of 421 patients with pulmonary tuberculosis reacted positive. Positive reactions were observed in 55.7% of 199 patients suffering from another infectious disease and in 31;7% of normal sera. Most precipitation lines were found with the antigen prepared from H37 Ra after incubation for 7 months. In human sera as well as in cattle a dependence of reactions upon mode of antigen production was evident.