The purpose of this experiment was to clarify the relationship between the serum vitellin producibility in estrogen administration and a few productive traits in laying hen i.e. the serum vitellin producibility was represented as b (the serum vitellin reaction regression coefficient) or b' (the regression coefficient calculated with the turbidities which was obtained from acetone precipitate of serum). Simultaneously, in this paper, the significance of the serum vitellin producibility at the viewpoint of poultry breeding was discussed.Four strains (Rape, Forsgate, Thornber and Garber) of White Leghorn chicken were employed in this experiment, and the total of them amounted to 327 birds (about 80 chickens in each strain). Estrogen administration of 0.4mg in daily does was practiced from 60 days of age and continued for 10 days. Blood sera collected from the chicken every day were used for observation of turbidity, and the regression coefficients (b') were estimated from the turbidity individually.Thereafter, they were reared for 4 months from the beginning of egg production and the records of egg laying were brought together.The relationships among the b', the egg weight at 300 day old, the body weight at 300 day old, the rate of egg laying for 4 months after the first egg, the number of egg laying to 300 day old and the age at first egg were examined each other.Least square means of each strain about the productive traits as above mentioned were estimated and Duncan's multiple range tests were employed to make all pairwise comparisons. The differences among strains for b' were non-significant, but significant in other traits.The correlations between the b' and the egg weight or the body weight at age of 300 days or also the age at first egg were significant, and these relations became more evident from the estimates of the partial correlations among each trait. However, the correlations between the b' and the rate of egg laying or the number of egg laying were non-significant respectively. Particularly, judging from the modes of frequency distribution as a bivariate normal population in regard to the b' and the rate of egg laying, it was unable to be considered as a normal distribution on account of the remarkable decrease of frequency of hen above 75% in the distribution of the rates of egg laying, as compared with the b' to be accepted as the random samples from a normal distribution. But, a small number of laying hen above 80% in the rate of egg laying was observed near the mean value of b'.On the other hand, the higher mortalities were observed in the groups showed low value in b' and the result of chi-square test was highly significant.From the results as above mentioned and various results during the past ten years, the correlations between the b' and some of the productive traits were recognized. However, it was suggested that the serum vitellin producibility represented as b or b' had close relation to physiological function in individual chicken and was an available guide for the detection of normal chicken in physiological function.