In order to prevent conception and/or infection by sexually transmitted diseases (STDs) one or more lectins capable of binding sperm or agglutinable components of male ejaculate and/or the pathogenic microorganisms responsible for STDs or the carbohydrate moieties expressed on cell surfaces by which the microorganisms bind to the cells, are administered to the vagina prior to sexual intercourse. The lectins prevent conception by binding to the sperm or agglutinable components of male ejaculate to render the sperm incapable of fertilization. They also bind to the pathogenic microorganisms to render them non-pathogenic or to carbohydrates expressed on cell surfaces to prevent infection by the microorganisms or treat such infections. Lectins can also be administered to treat sexually transmitted vaginal infections. The lectins can also be applied to or contained within a condom. The condom may carry the lectins either within the hollow interior of the condom or impregnated into, linked to, or coated upon its membrane body. Lectins may also be incorporated in the same way into a surgical glove for protection against infection by pathogenic microorganisms.