The purpose of the present work is to clarify the mechanism of egg-yolk deposition in the ovary by means of a biochemical method. This paper deals with the nucleic-acid contents of the liver as a site of synthesis of the yolk-precursor, a hormonal stimulator of the synthesis, and the relationship between serum protein and the nucleic-acid content of the liver. The results obtained are summarized as follows.<br>1. In the first experiment, the average content of desoxyribonucleic acid (DNA) per 100g of fresh liver tissue was smaller in the laying hen than in other groups, but that of ribonucleic acid (RNA) per 100g of fresh liver tissue was larger in the laying hen than in the others. The ratio of RNA to DNA (RNA/DNA) in the liver was higher in the laying hen than in the non-laying hen and cock (P<0.05). The total DNA contained in the whole liver was not significantly different among the three groups. The total RNA contained in the whole liver, however, was significantly more in the laying hen than in the non-laying hen and cock (P<0.05 in either case). Phosphoprotein phosphorus was found abundantly in the serum of the laying hen, but was hardly detected from the sera of the non-laying hen and cock. The content of phosphoprotein phosphorus in the liver was higher in the laying hen than in any other group, the difference between the laying hen and either group being highly significant.<br>2. In the second experiment, estrogen treatment accounted for the increase in liver weight. The liver increased in weight in direct proportion to the dosage of estrogen given. In accordance with the increasing dosage of estrogen, the DNA content per 100g of fresh liver tissue decreased, but the RNA content increased. The ratio of RNA/DNA in the liver was significantly greater in the estrogen-treated cockerel than in the untreated control. The total content of DNA the whole liver increased slightly and that of RNA increased greatly by the estrogen treatment.<br>3. The content of crude protein in the serum was larger in the estrogen-treated cockerel than in the control and increased in accordance with an increase in the dosage of estrogen. The coefficient of correlation between the crude protein of serum and the ratio RNA/DNA of the liver was+0.918 (P<0.05). The phosphoprotein phosphorus of serum was hardly found in the control, but was abundant in the estrogen-treated bird. The content of phosphoprotein phosphorus of the liver was larger in the estrogen-treated groups than in the control. It increased in accordance with an increase in the dosage of estrogen in all the treated groups, except one injected with 1.0mg. The results obtained from experiments carried out with White Leghorns in the same manner were essentially the same as those with cross-breds.