Abstract
Fertilization of mouse, rat and hamster eggs can be inhibited by a single intraperitoneal injection of respective anti-ovary antiserum obtained from rabbits. These anti-ovary antisera absorbed with the ovary did not prevent fertilization but antisera absorbed with the liver and kidney inhibited fertilization of mice and hamsters but not that of rats. Fertilization in rats and mice was not inhibited by a single intraperitoneal injection of anti-ovary antiserum obtained from isoimmunized rats and mice respectively but in vitro fertilization of mouse eggs was inhibited in the presence of such isoimmune anti-mouse ovary antiserum.