Participants are divided into 4 cohorts depending on their serostatus and whether they are the insertive or receptive partner. Participants apply Advantage 24 once or twice a day for 5 weeks and 4 times a day for the sixth week. Check-in visits, which include a genital exam, are performed at Weeks 1, 2, 4, 5, and 7. More complete physical evaluations, including anoscopy for receptive partners and blood tests, are performed at Weeks 3, 6, and 8.