We detected the HBV DNA in peripheral blood monocytes of 70 patients with chronic hepatitis B and 20 healthy controls by polymerase chain reaction (PCR) and Southern transfer hybridization technique, the HLA-DR expression on monocytic membrane and tumor necrosis factor-alpha (TNF alpha) content and interleukin 1 (IL 1) activity in their monocytic culture supernatant were also measured respectively by indirect immunofluorescence technique, ELISA, and thymocytic multiplication assay. HBV DNA sequences were detected in monocytes of 42(60%) of the 70 patients. The percentage of monocyte-expressing HLADR and the TNF alpha content in monocyte culture supernatant were significantly elevated in patients with HBV DNA-positive monocytes compared with those patients with HBV-DNA-negative monocytes. The percentage of monocyte-expressing HLA-DA and the level of TNF alpha produced by monocytes correlated markedly with the intensity of HBV DNA-positive signal in monocytes. These data suggested that HBV infection in monocytes might cause a series of functional changes in these cells.