- ART-experienced subjects are defined as having had greater than 4 weeks (28 days) therapy with any NRTI(s) and any length of therapy with any NNRTI(s) and/or a PI. PI-experienced subjects will be eligible if they have previously been treated with < three PIs, excluding AGENERASE. Prior therapy with a RTV boosted PI regimen will be considered as only 1 prior PI as long as the RTV dose was below that recommended for use of RTV as an antiretroviral agent. This specific criterion is not applicable to subjects in screening and/or enrolling after approval of Amendment No. 4. - For subjects screening and/or enrolling after the approval of Amendment No.4, PI naive subjects are defined as ART experienced subjects having less than one week of therapy with a PI and no prior experience with AGENERASE. Prior treatment with NNRTIs and NRTIs is permitted (however, subjects will NOT be permitted to receive concurrent NNRTI therapy while participating in this study)