Coitus provides the repeated inoculation of the female reproductive tract with powerful seminal antigens. Basic studies of the natural processes involved in the prevention of immunological sensitization of normal female with seminal antigens and occasional failures of these natural safeguards may have tremendous application in simulation of immune-infertility for contraception and regulation of immune response. An inhibitor of immune response of seminal origin has been implicated in the prevention of sensitisation of females. This project aims at purification and characterization of this inhibitor, studies on the site of its synthesis in the male reproductive tract, cellular and molecular mechanism involved in the inhibition of immune response and finally the role of the inhibitor in the etiology of immune-infertility.