 - HIV-1 RNA undetectable by ultrasensitive assay copiesml obtained at study screening visit or within 60 days prior to study screening visit performed with an ultrasensitive HIV-1 PCR assay. All subjects must have received at least 18 months of therapy and have HIV-1 RNA 50 copiesmL using a FDA-approved assay for at least 48 weeks prior to enrollment. HIV-1 RNA must be measured at least once in the 24 weeks prior to enrollment and at least 3 days before the screening measure. Single determinations that are between 50 and 500copiesmL i.e., blips are allowed as long as the preceding and subsequent determinations are 50 copiesmL. The screening value may serve as the subsequent determination 50 copiesmL following a blip. NOTE: subjects who have participated in other trials using ATIs will be permitted since detectable virus during the interruption does not represent virologic failure. These subjects should have at least 24 weeks of VL 50 copiesmL. 