Patients are assigned to one of four groups. Three dose groups receive a background antiretroviral regimen (ABC, APV, RTV, and EFV) and T-20, which is given at one of three doses on a twice-daily regimen. The fourth group (control) receives the background antiretroviral regimen alone. For each treatment group, 17 patients are enrolled. Treatment is administered for 16 weeks, followed by a 32-week treatment extension, and a 2-week follow-up period. The following are assessed throughout the trial: safety parameters (as measured by hematology, clinical chemistry, urinalysis, and treatment-emergent adverse events); virologic and immunologic activity; phenotypic and genotypic resistance; T-20 plasma levels; and pharmacokinetics of T-20 and oral antiretrovirals. The total study duration is 1 year.