WE have found a simple method for the preparation of a mixture of ribonucleic acid and deoxyribonucleic acid and the preparation of purified deoxyribonucleic acid in a highly polymerized state from cells of M. lysodeikticus. In arriving at the techniques, we have taken advantage of the fact that above pH 8.0 the activity of the ribonuclease system in M. lysodeikticus is negligible. Moreover, in the absence of orthophosphate, polynucleotide phosphorylase (polyase) is inactive toward ribonucleic acid. Therefore, for maximum yields of ribonucleic acid the lysis of the cells was carried out at pH 8.5. To destroy the ribonucleic acid selectively orthophosphate was added1. This communication presents some of the preliminary results.