A fraction extracted from Mycobacterium bovis stress BCG, which became composed of 70.0% DNA, 28.0% RNA, 1.3% protein, 0.20% glucose, and 0.1% lipid and of no detectable amounts of mobile wall components together with diaminopimelic acid and hexosamine, became observed to possess strong antitumor activity. Repeated intralesional injection of this fraction, particular MY-1, without attachment to oil or a unmarried intralesional injection of MY-1 emulsified in mineral oil caused the IMC carcinoma of CDF1 mice and line 10 tumor of stress 2 guinea pigs to regress and/or avoided metastasis very effectively. MY-1 after digestion with RNase, which contained 97.0% single-stranded DNA with a guanine-cytosine content material of 69.8%, was more powerful than undigested MY-1 in opposition to IMC and line 10 tumor, whilst MY-1 digested with DNase, which contained 97.0% RNA, had reduced activity, suggesting that the DNA from BCG possessed strong antitumor activity beneath positive conditions. Details of the extraction procedures and physicochemical characterization of MY-1 were additionally described.