A method is disclosed for reducing the risk of infection by sexually transmitted viruses. This method involves spreading a lubricant fluid containing a selected zinc salt across the surfaces of the penis or vagina, before intercourse, in a manner that causes the lubricant to coat and remain in contact with the genital surfaces throughout intercourse. The zinc salt should be organic, water-soluble, non-irritating, physiologically acceptable, and have a high rate of dissociation, which allows it to release substantial quantities of divalent zinc ions. Suitable zinc salts include zinc acetate, zinc propionate, zinc butyrate, zinc formate, zinc gluconate, zinc glycerate, zinc glycolate, and zinc lactate. A preferred carrier fluid comprises a lubricant gel, which also contains water, a thickening agent (such as chemically treated cellulose) and a lubricating agent (such as glycerin). The lubricant formulation must be free of heparin, dextran sulfate, or any other component that poses a substantial risk of adverse effects if the lubricant is used frequently and repeatedly over a period of months or years. The lubricants disclosed herein preferably should be used with condoms, to enhance the risk-reducing effectiveness of condoms and provide maximum protection; however, these lubricants can also be used without condoms, if desired.