Highly active antiretroviral therapy (HAART) regimens containing PIs, NNRTIs, or nucleoside reverse transcriptase inhibitors (NRTIs) have been shown to slow disease progression. However, the long-term consequences of initial therapy with a PI, an NNRTI, or both a PI and an NNRTI are not yet known, nor is the impact on future anti-HIV treatment regimens. Patients who experience virologic failure on a particular HAART regimen typically have not been studied for subsequent response to other HAART regimens. It is possible that a regimen which is initially the most potent may not be optimal if it limits the effectiveness of subsequent anti-HIV treatment regimens.