45 women and 45 men, all healthy and sexually active, 21-45 years old, without HIV infection, will be enrolled in Francistown and Gaborone, Botswana. Volunteers will be randomized to receive either 0.1% or 0.25% UC-781 carbomer gel or placebo gel (3 arms. Women will be instructed to apply gel intravaginally, morning and evening, and prior to sex (always with male condom use) for 14 consecutive days. Men will be instructed to apply gel topically for 14 consecutive nights, before bed, allow to dry overnight, and wash it off in the morning. Additionally instructed never to use gel during sex but always to use condoms. Volunteers will be seen weekly for evaluation of symptoms, laboratory toxicities, genital exam findings (with colposcopy for women, and plasma drug levels. Acceptability will be assessed in focus groups in the month after completing gel use.