This study will compare the response of subjects who failed a first-line ATV-containing regimen and who have the 150L-containing virus to subsequent protease inhibitor (PI)-containing therapy with that of a cohort who has failed a first-line reverse transcriptase inhibitor (NNRTI), and is subsequently receiving PI-containing therapy.

Inclusion Criteria:

• Currently on a first-line antiretroviral regimen containing ATV with a confirmed rebound and a genotype that verifies the presence of an 150L mutation OR on a first-line regimen containing an NNRTI and PI-naive, with a confirmed rebound

Exclusion Criteria:

• Women of child bearing potential who are unwilling or unable to use an acceptable method to avoid pregnancy for the entire study period and for up to 8 weeks after the study.
• Women who are pregnant or breastfeeding.
• A life expectancy of <12 months.
• Presence of a newly diagnosed HIV-related opportunistic infection or any other medical condition requiring acute therapy at the time of enrollment.
• Active alcohol or substance abuse sufficient, in the investigator's opinion, to prevent adequate adherence to study therapy or to increase the risk of developing pancreatitis or chemical hepatitis.

HIV infected individuals on first line ATV based HAART with presence of I50L mutation & HIV infected PI naïve on failed NNRTI based regimen.