Abstract: Forty-five C57BL/6J female mice were mated with the same strain male.3 μl mixture of undiluted H-Y antisera and guinea pig complement (1∶2) were injectcd into each uterine horn of the female mice,while into each uterine horn of control female mice only 3 μl complement was injected.In consequence,247 offsprings were obtained from 42 of 45 experimental female mice:each litter has 6 offsprings on average,the sex ratio was 2.7 (180♀/67♂),and its percentage was 73%;163 offsprings were obtained from 20 contrel femal;mice:the average of each litter was 8 offsprings,the sex ratio was 0.92(78♀/85♂),and its percentage was 48%.Obviously,the percentage of the fcrmer was 25% higher than that of the latter.The difference betwecn them was very significant (P<0.001).