The primary endpoint is the the safety and tolerability of RAL 400 mg b.i.d. in combination with OBT, assessed by review of the accumulated safety data in HIV-infected adult patients. The secondary endpoint is antiretroviral activity of RAL 400 mg b.i.d. in combination with OBT as measured by change at week 24 in viral load from baseline, increase of CD4+ T lymphocytes compared to baseline and proportions of patients with: viral load less than 400 copies/ml; viral load less than 50 copies/ml; and a reduction in viral load from baseline exceeding 1.0 log10 copies/ml.