An OB regimen is selected to be initiated at baseline by the physician and patient. The OB regimen is based on the patient's prior treatment history as well as the results from the first screening visit HIV-1 genotypic and phenotypic (GT and PT) resistance testing and prior GT/PT antiretroviral resistance testing (if available). Prior or current laboratory abnormalities, including triglycerides and cholesterol, should also be taken into account when selecting the OB regimen. Patients are stratified with respect to the following: 1) screening viral load (less than 40,000 or 40,000 or more copies/ml); and 2) number of allowed investigational antiretrovirals (0, 1, or 2). Patients then are randomized to receive 1 of the following treatments for 48 weeks: OB regimen or OB plus T-20 regimen. Patients are seen for evaluation of efficacy and safety at Weeks 1, 2, and 4, every 4 weeks through Week 24, and then every 8 weeks through Week 48. In addition, efficacy only is evaluated at Weeks 6, 10, and 14. Patients also may be seen at additional visits during the study for plasma HIV-1 RNA measurements to potentially confirm virological failure.

Patients initially randomized to the OB arm who meet the criteria for virological failure and who switch to OB plus T-20 after Week 8 are followed under a new ("switch") schedule of assessments. Patients are encouraged to change their OB regimen at the time of switch.

Patients initially randomized to the OB plus T-20 arm who meet the criteria for virological failure may continue to receive OB plus T-20 if the patient and the physician feel that there is sufficient benefit. Patients are encouraged to change their OB regimen after Week 8 if they choose to continue on OB plus T-20 despite meeting the criteria for virological failure.

Patients on OB or OB plus T-20 arm who meet the criteria for virological failure but who do not wish to either switch to T-20 (for patients initially randomized to OB arm) or continue with T-20 (for patients initially randomized to OB plus T-20) are allowed to remain in the study for a maximum of 1 month.

At the end of the 48 weeks of treatment, patients are allowed to participate in 1 of the following treatment extensions: a) roll-over and receive OB plus T-20 (for patients receiving OB alone); or b) continue taking OB plus T-20 (for patients already receiving OB plus T-20), for a maximum of an additional 48 weeks (plus 4 weeks safety follow-up period), or until 12 weeks after commercial availability of T-20 in the country in which they are treated, whichever comes first. All patients are followed for a maximum of 100 weeks from their initial baseline visit date.