 PRO 140 is a man-made monoclonal antibody to the chemokine receptor CCR5, which serves as a co-receptor for HIV. In numerous preclinical models of HIV infection, PRO 140 broadly and potently blocks CCR5-mediated HIV entry without blocking the natural activity of CCR5. PRO 140 is being developed for therapy of HIV infected individuals. The purpose of this study is to evaluate the safety and tolerability of PRO 140 in HIV uninfected male volunteers. The pharmacokinetics and pharmacodynamics of PRO 140 will also be assessed in this study. 