Most of the tests have been carried out with rat liver, but similar results have been obtained with rat kidney, spleen, testis, a hepatoma and calf thymus glands. The tissue was homogenized with isotonic solutions of the salts, adjusted to pH 6*5 in order to avoid complications by release ofnuclear materials through osmotic or pH effects. DNA was liberated when potassium cyanide or ethylenediamine was used at pH 10, but remained insoluble if the pH was 6-5.