In the earlier works from this laboratory, biosynthesis, acetylation, methylation and phosphorylation of histone of transplantable ascites tumor cells have been studied. The present paper deals with the effects of X-ray irradiation on histone biosynthesis of Sarcoma 180 ascites tumor cells. The tumor-bearing mice were irradiated with a dose of 1250 roentgen prior to 24 hours double-labeling with $10;{mu}Ci$ of glycine-$^{14}C$ and $20;{mu}Ci$ of $^{32}P$-orthophosphate. Sham irradiated mice were used as control. Histones were prepared by Johns procedure and fractionated on polyacrylamide disc gel electrophoresis. The histones were hydrolyzed in acid and the digests were chromatographed on an amino acid analyzer. DNA was extracted according to the method of Ogur and Rosen. Radioactivity was counted in a liquid scintillation spectrometer. The time course changes in the incorporations of labeled compounds into histone and DNA have been followed. Results obtained were as follows; 1. Contents of histone fractions from Sarcoma 180 ascites tumor cells have been shown to markedly differ from normal tissues, i.e. mouse liver, rat and calf thymus. 2. X-ray irradiation hindered $^{14}C$-glycine incorporation into histone by 14 per cent. Uptake of $^{14}C$ was highest into f3 and was lowest into f2b among histone fractiones both in normal and irradiated mice. The incorporation of $^{14}C$-glycine into histone reached a maximum 4 hours after glycine administration. 3. Radioactivity of $^{14}C$-glycine was less distributed about 12 per cent in glycine fraction of histone hydrolysates from X-ray irradiated animal. 4. A decreased $^{32}P$-incorporation (about 14%) into DNA was observed in irradiated mice. Relationships between histone biosynthesis and DNA metabolism were also discussed.