Several studies from this laboratory have in the past few years dealt with the chemistry of nucleic acids. (For recent summaries, see Chargaff (1, 2).) The development of precise micromethods for the separation and quantitat,ive estimation of the purines and pyrimidines has made possible the investigation of a large number of different nucleic acid preparations. These studies led to the conclusion that the desoxypentose nucleic acids (DNA) exhibited a composition that in many cases differed very considerably (3, 4) from that of calf thymus DNA (5). The present paper provides information on the composition of,the highly polymerized DNA from the spermatozoa of the salmon (Xalmo s&r) and compares the results obtained with two different hydrolysis methods employed in this laboratory.