In the earlier works from this laboratory, biosynthesis, acetylation, methylation and phosphorylation of histones of transplantable ascites tumor cells have been studied, Present paper deals with the effects of Y-irradiation on histone and DNA of sarcoma 180 a.scites tumor cells. The tumor-bearing mice were Y-irradiated with a dose of 1250 roentgens prior to 24 hours double-labeling with 10 uCi of glycine-l-^(14)C and 20 uCi of ^(32)P-orthophosphate. Sham-irradiated mice were used as control. Histones were prepared by Johns procedure and fractionated on polyacrylamide disc gel electrophoresis. DNA was extracted according to the method of Ogur and Rasen. Radioactivity was counted in a liquid scintillation spectrometer. The time course changes in the incorporations of labeled compounds into histone and I)NA have peen followed Results obtained were as follows ; 1. A decreased ^(32)P-incorporation (about 14%) into DNA was observed in irradiated mice. 2. The incorporation of ^(14)C-glycine into histone reached a maximum 4 hours after gll;cine administration. Gamma-irradiation hindered ^(14)C-glycine incorporation into histone by 14%. Uptake of ^(14)C was highest into f3 and was lowest into f2b among histone fractions both in normal and irradiated mice. Radioactivity of ^(14)C-glycine was distributed about 12% in glycine fraction of histone hydrolysates.