Although a change in reverse transcriptase (RT) inhibitors is recommended when adding or changing protease inhibitors in a treatment regimen, the choice of available RT inhibitors is often limited by prior exposure, toxicity, or pharmacologic interaction with the protease inhibitors. This study addresses the question of whether to continue 3TC or substitute the nonnucleoside reverse transcriptase inhibitor (NNRTI) DLV when adding IDV to therapy for patients previously treated with ddI or d4T plus 3TC who have greater than 500 copies/ml of plasma HIV-1 RNA. Although the activity of DLV as monotherapy or in combination with nucleoside reverse transcriptase inhibitors is of limited duration due to rapid emergence of resistance, it is possible that DLV will contribute significantly to the activity of 3-drug regimens that include a new RT inhibitor plus a protease inhibitor.