TBR-652 is a novel CCR5 antagonist with potent in vitro anti-HIV activity. The objective of this study was to determine the pharmacokinetics (PK) and pharmacodynamics (PD) of TBR-652 in HIV-1-infected, antiretroviral treatment-experienced, CCR5 antagonist-naive patients. A double-blind, placebo-controlled, randomized, dose-escalating study of TBR-652 monotherapy given once daily orally for 10 days was performed followed by a 40-day follow-up period.