Modified hormones or fragments of hormones are useful in producing antibodies when administered to an animal. Said antibodies in turn cause neutralization of endogenous natural protein hormones. The modification may be accomplished by attaching various kinds of modifying groups to the hormone or fragment. Modification may, for example, be achieved by chemically coupling diazosulfanilic acid groups to the hormone or fragment. The protein hormones to which this procedure can be applied are mammalian protein reproductive hormones such as, for example, Follicle Stimulating Hormone (FSH), or Human Chorionic Gonadotropin (HCG). These modified polypeptides may be administered to animals for the purpose of contraception, abortion, or treatment of hormone-related disease states and disorders, including hormone-associated carcinomas.