1. 1. To evaluate the relation of the heterochromatic chromosome regions to the nucleic acids, a comparison has been made of the nature and the amount of the ribonucleic acids in two types of unfertilized Drosophila melanogaster eggs; one, the normal wild type (XX), and the other containing the Y chromosome attached to one of the X's ( X XY sc8 ). 2. 2. The proportions of the purine and pyrimidine bases present in purified ribonucleic acids from both types of egg has been determined. 3. 3. The X XY sc8 type RNA contains a significantly higher proportion of adenine than does the XX RNA. 4. 4. The ultraviolet absorption curves of hydrolysates of the two types of RNA correspond to those expected for a mixture of nucleotides calculated from the analysis of the respective base compositions. Both before and after hydrolysis, the X XY sc8 RNA has a higher specific absorption than does the XX, in conformity with its higher content of adenine. 5. 5. The quantity of RNA per egg is substantially equivalent in the XX and the X XY sc8 types. 6. 6. In the light of the new chemical data, earlier measurements of the effect of the Y chromosome on the cytoplasm of the egg are now interpreted as indicating an effect of the Y on the composition instead of the amount of RNA in the egg cytoplasm. In this way, the hypothesis of a relation between the heterochromatic regions and the nucleic acid metabolism of the cell receives new support.