This 2 arm study will assess the efficacy and safety of a new regimen of Fuzeon

+ optimized background antiretroviral treatment, in Fuzeon-naive HIV-1 infected patients with virological failure. Eligible patients will be randomized to recei ve either new optimized treatment alone, or optimized treatment + Fuzeon 90mg s.

c. twice daily, to determine the effect of 3 month induction with Fuzeon.It will be possible for a patient to receive several additional 3 month periods with F uzeon, in the case of new virological failure. The anticipated time on study tre atment is 3-12 months, and the target sample size is <100 individuals.

Inclusion Criteria:

• adult patients, >=18 years of age;
• HIV-1 infection, with virologic failure;
• on same stable HAART for >4 weeks, with viral load >1000 RNA copies/mL;
• Fuzeon-naive.

Exclusion Criteria:

• coinfection with HIV-2;
• active opportunistic infection in 4 weeks prior to screening;
• cirrhosis or severe liver failure;
• severe renal disease.