A single infusion of an HIV antibody called VRC01 suppresses the virus in people not taking antiretrovirals (ARVs), persists in the body for some time, and is safe and well tolerated. In a Phase I trial of VRC01, the eight participants who were on ARVs received two infusions of the antibody, spaced 28 days apart. The 15 people who were not taking ARVs received one infusion.VRC01 did not reduce the amount of virus in blood cells, but it did reduce viral load by more than 10-fold in six of the people not on ARVs. In this group of six, the two people who started the study with the lowest viral loads developed undetectable viral loads for about three weeks. The remaining four people experienced a substantial viral load reduction, but not to undetectable levels. Among those taking ARVs, the antibody appeared to have no effect.