We examined hepatitis C virus (HCV) RNA levels in serum, peripheral blood mononuclear cells (PBMC), and the liver for 135 patients with chronic HCV infections, 44 of whom were human immunodeficiency virus (HIV) positive and treated with highly active antiretroviral therapy (group A), 66 of whom were HIV negative (group B), with abnormal serum alanine aminotransferase (ALT) values, and 25 of whom were HIV negative, with ALT values of </=1.5 times the normal value (group C). Patients had not been treated with interferon, with or without ribavirin, at the time of the study. A statistically significant correlation between HCV RNA levels in the liver and serum was reproducibly documented, whereas this was inconsistent for serum and PBMC. A comparative evaluation of HCV RNA levels in the liver and PBMC showed significantly lower values for group A than for groups B and C (P < 0.01 and P < 0.0001, respectively). In contrast, HCV RNA levels in serum were significantly higher for group A than for group B (P < 0.001). A dissociation between HCV RNA levels in serum and the liver was found for patients with HIV-HCV coinfections. Although the relative contribution of extrahepatic reservoirs, including lymphoid cells, to HCV RNA levels in serum is unclear, it may be speculated that a low intrahepatic HCV burden is caused by restored immunocompetence after successful antiretroviral therapy in coinfected patients.