The preparation of a deoxyribonucleoprotein from the BCG variant of bovine type tubercle bacilli is described. The principal steps involved precipitation at pH 4.2, removal of contaminating materials at half-saturation with ammonium sulfate, and fractionation with ethanol at a low temperature. The purified product was shown to contain about 0.4 amino acid residue for one nucleotide residue. An approximate estimation of the principal amino acids contained in the nucleo-protein revealed a preponderance of dicarboxylic over basic amino acids. The deoxyribonucleic acid was freed of its protein component by tryptic digestion and examined with respect to the distribution of purines and pyrimidines. It belongs to the extreme “GC type”. More detailed aspects of the arrangement of nucleotides in the nucleic acid chain were studied through the application of the method of differential distribution analysis, making use of the results of the stepwise acid hydrolysis. The sugar moiety of the deoxypentose nucleic acid was identified tentatively as deoxyribose. The nucleotide composition of the pentose nucleic acid of BCG also was determined.