To maximize the likelihood of a favorable response to salvage therapy, 4 or 5 drug regimens should be studied. Regimens containing fewer drugs, particularly those lacking a non-nucleoside reverse transcriptase inhibitor (NNRTI) such as efavirenz, are likely to result in an unacceptable rate of virological failure. Therefore, this study examines drug combinations which include two new nucleoside reverse transcriptase inhibitors (NRTIs), the NNRTI efavirenz, and either one or two protease inhibitors which are known not to produce cross-resistance to nelfinavir.