A synthetic peptide capable of eliciting antibodies that neutralize human chorionic gonadotropin**This work was undertaken as part of the contraceptive development research program sponsored and coordinated by the International Committee for Contraception Research of the Population Council, Inc., New York, New York. The financial support provided by the International Development Research Center of Canada, The Ford Foundation, The Rockefeller Foundation, and the George J. Hecht Fund is gratefully acknowledged.