Over the past 18 years, the WHO Task Force on Vaccines for Fertility Regulation has been supporting basic and clinical research on the development of birth control vaccines directed against the gametes or the preimplantation embryo. These studies have involved the use of advanced procedures in peptide chemistry, hybridoma technology and molecular genetics as well as the evaluation of a number of novel approaches in general vaccinology. As a result of this inter national, collaborative effort, a prototype anti-HCG vaccine is now undergoing clinical testing, raising the prospect that a totally new family planning method may be available before the end of the current decade.