A number of studies both within and outside the ACTG have been initiated or are in development to try to address the issue of alternative treatments for patients who either do not achieve or lose virologic control while receiving protease inhibitors (PIs). Amprenavir (APV) is an attractive candidate to investigate as part of salvage regimens because: 1) it has substantial antiretroviral activity; 2) there are preliminary in vitro and in vivo data that suggest that resistance to this agent may be mediated in part by a unique mutation (I50V); and 3) its cross-resistance profile to the approved PIs is uncertain.