HCV infection is known to cause morbidity and mortality especially among those who are coinfected with HIV. The underlying immunopathogenesis of persistence of HCV infection, progression of liver disease and interactions with HIV are not yet clearly understood. A clear understanding of the immune correlates of protection against HCV would definitely be important in development of a vaccine for HCV. HCV infected individuals who are also coinfected with HIV have more rapid progression of liver disease, abnormal diagnostic serologies, higher levels of HCV viremia and markedly lower levels of therapeutic responses to the standard combination therapy with peginterferon and ribavirin. This study will recruit individuals who are coinfected with both HIV and HCV as well as those who are monoinfected with HCV. The study will require that patients be apheresed several times after enrollment. Apheresis will be necessary in order to obtain sufficient cells to pursue the following objectives: delineating B cell response to CD4+ T cell help, delineating CD8+ T factors associated with suppression of viral replication and normalization of immune function, and characterizing natural killer function relative to HCV disease and identify biomarkers for prgression of liver disease. The required number of mononuclear cells needed to perform these experiments can be easily and safely obtained using apheresis procedures in the Clinical Center Apheresis Unit. All patients will receive a liver biopsy (every 3 years for co-infected and every 5 years for mono-infected) subjects to assess the progression of liver disease performed at the NIH.