This study will examine how quickly white blood cells called CD4 lymphocytes reproduce and how long they live in people infected with HIV. It will do this using bromodeoxyuridine (BrDU), a compound that is structurally similar to thymidine, one of the building blocks of DNA. BrDU gets incorporated into DNA instead of thymidine, but it can only get into cells that are replicating. Therefore, measuring the proportion of cells with BrDU indicates how many cells are replicating.