The presence of HCV RNA in peripheral blood mononuclear cells (PBMC) has been reported. To identify the cell populations carrying HCV RNA, the presence and amount of HCV RNA was investigated by limiting dilution nested reverse transcriptase-polymerase chain reaction (PCR) in PBMC subpopulations fractionated by automated cell sorting. Fifteen chronically HCV-infected patients were included in the study, 4 of whom also had mixed cryoglobulinemia. HCV RNA was present in the CD19 cells of all 15 patients, but only 5 (35.7%) of 14 and 5 (41.6%) of 12 showed HCV RNA in CD3 and CD14 cells, respectively (P < .001 by Fisher's test for each comparison). The median titer of HCV RNA was 1 PCR unit/380 CD19 cells, compared with median of 1 PCR unit/6600 PBMC as a whole. Titration was difficult in the CD3 and CD14 cells because of the frequent negativity of the first diluted sample. This study suggests that HCV RNA is selectively concentrated in B cells.