LIVER RIBONUCLEIC ACID 3792. The nucleic acid is free from protein and from desoxypentose. It resembles yeast ribonucleic acid in its pentose content, in its absorption spectrum, in its action as a substrate for ribonuclease and in its content of purine and easily hydrolyzable phosphorus. Among the hydrolysis products d-ribose has been identified as the p-bromophenylhydrazone.We should like to thank Dr Neil Campbell of Edinburgh University for supplying us with a specimen of pure pbromophenylhydrazine, and for his advice on the preparation of hydrazones. This work was carried out during the tenure of a Carnegie Teaching Fellowship by one of us (J.N.D.). A grant for scientific assistance from the Medical Research Council and an expenses grant from the Carnegie Trust for the Universities of Scotland to one of us (J.N.t.) are gratefully acknowledged.