Highly active antiretroviral therapy has revolutionized the care of patients with HIV infection, but treatment is often complicated by the development of antiretroviral resistance. CCR5 inhibitors are a novel class of antiretroviral agents that block the CCR5 receptor, thereby preventing HIV-1 recognition and entry into CD4+ macrophages and T-cells. Schering-Plough Corp is developing vicriviroc, a CCR5 inhibitor that has demonstrated good oral bioavailability, has a long half-life that allows once daily dosing, and is primarily metabolized by cytochrome P450 CYP3A4. In vitro and clinical data suggest that vicriviroc has excellent antiviral potency with minimal toxicity. Phase I and II clinical trials demonstrated promising efficacy results when vicriviroc is administered to patients infected with CCR5-tropic HIV-1. At the time of publication, phase III trials were ongoing or planned to investigate the efficacy and safety of vicriviroc in antiretroviral-naïve and -experienced patients infected with HIV-1.