From 2008 to 2009, blood samples will be collected from consecutive HIV-1-infected patients who received HIV care at the National Taiwan University Hospital. We expect to collect 100 cases who are antiretroviral naïve and 100 cases who are treatment-experienced patients. A standardized case collection form will be used to record data of demographics and clinical characteristics and laboratory results, such as plasma HIV RNA load (PVL) and CD4 cell counts. PVL will be quantified by the Cobas Amplicor HIV-1 MonitorTM Test, version 1.5, (Roche Diagnostics Corporation, Indianapolis, USA) according to manufacturer's protocol. The CD4 cell count will be determined using FACSFlow (Becton Dickinson). This study was approved by the Institutional Review Board of the hospital.