Have adequate blood counts (HIV positive volunteers: hemoglobin greater than or equal to 9.0 g/dL, HCT greater than or equal to 28%, platelets greater than or equal to 50,000; HIV negative healthy normal volunteers: hemoglobin greater than or equal to 12.5 g/dL, HCT greater than or equal to 38%, platelets greater than or equal to 150,000.