Abstract
1. A technic for the study of fixed preparations of blood and bone marrow by means of fluorescence microscopy with acridine orange is presented. 2. The distribution of RNA and DNA within the blood cells can be demonstrated cytochemically. 3. The RNA content of the erythroid and myeloid cells decreases with maturation. Mature plasma cells contain large quantities of RNA. 4. It is possible to demonstrate cytoplasmic metachromasia between the AO-RNA complexes of the erythroid, myeloid, and plasmacytic cells.