The presence of paternal H-2 antigens on hybrid mouse blastocysts during experimental delay of implantation and the disappearance of these antigens after onset of implantation.

The presence of paternal H-2 antigens on hybrid mouse blastocysts before and during implantation was investigated by means of the isotope anti-globulin technique. It was found that experimentally delayed blastocysts possess paternal H-2 antigens whereas these antigens can no longer be detected 14 hours after estradiol activation of delayed blastocysts.