The presence of separate desaminases for ribosenucleic acid (RNA) and for desoxyribosenucleic acid (DRNA) is estab. in several animal tissues. The enzymes split 2 atoms ammonia N/tetranucleo-tide from each nucleate, and act upon the latter without preliminary degradation of the molecule. The enzymes are heat-labile and can be distinguished as follows: the desami-nase activity for DRNA is diminished more rapidly by dilu-tion than is that for RNA, fluoride inhibits the desamination of DRNA but not that of RNA, and dialysis produces loss of capacity of the tissue to desaminate DRNA but not that of RNA. The capacity to desaminate DRNA can be restored to the dialyzed extract by adding any one of the following items: Li, Na, K, Rb, Cs, Mg, Ca, Ba, Sr, Co++, Fe++, Ni++, and guanidinium. The desaminases for adenylic acid, guanosine, and guanine are distributed in tissues differently from those of the nucleates.