(PE)HRG214 (HRG) is a polyclonal antibody preparation produced by immunization of goats with purified human immunodeficiency virus (HIV) antigens. In this phase I study, HRG was administered intravenously as a single dose (1, 2, 4, 8, or 16 mg/kg) to 18 HIV-1-infected patients with CD4 cell counts >/=50 cells/microL and virus loads >/=500 copies/mL. The most frequent adverse event was a transient rash, which appeared to be both dose- and CD4 cell count-dependent. At the 16 mg/kg level, median half-life was 68.4 h, and median C(max) was 392 microg/mL, a level well above that which inhibits HIV in vitro. At that dose level, median and maximum decreases in HIV-1 RNA levels at day 8 were 0.24 log(10) and 0.58 log(10), respectively, and, at day 29, were 0.24 log(10 ) and 2.2 log(10), respectively. HRG, administered as a single dose, is reasonably well tolerated and achieves adequate plasma concentrations.