Combination antiretroviral therapy can offer patients potent suppression of HIV replication and improved immunologic functioning. However, despite aggressive antiretroviral regimens currently in use, only about 50 to 60 percent of patients attain plasma viral loads below 50 copies/ml after 24 weeks. Initiating treatment with a 4-drug regimen may increase this percentage, but this may also contribute to patient non-adherence, drug-related toxicities, potential cross-resistance to drugs used in future regimens, and high financial costs. Another strategy is early intensification (adding a single drug to an existing regimen) in patients who are at risk for attaining incomplete viral suppression after 24 weeks of therapy. ABC may produce a significant antiviral effect when used as an intensification agent in patients on a stable antiretroviral regimen. The results of this study will offer insight into the potential benefits of early treatment intensification.