Influence of hepatitis delta virus replication in the presence of hepatitis B virus DNA in peripheral blood mononuclear cells. The presence of hepatitis B virus DNA was studied in peripheral blood mononuclear cell samples from 259 HBsAg carriers (229 anti-hepatitis delta negative, 30 anti-hepatitis delta positive), 16 anti-HBc-positive HBsAg-negative patients and 30 patients without hepatitis B virus markers. Hepatitis B virus DNA sequences were detected in peripheral blood mononuclear cell from 115 (44.4%) of the chronic HBsAg carriers and from two (12%) of the anti-HBc-positive, HBsAg-negative patients. In anti-hepatitis delta-negative patients, viral DNA was positive in peripheral blood mononuclear cell from 74 (46%) and from 24 (35.5%) with and without serum HBV-DNA, respectively. With respect to anti-hepatitis delta-positive patients, viral DNA was found in peripheral blood mononuclear cell in 8 of 13 (61.5%) of the patients with circulating hepatitis delta virus RNA and in 9 of 17 (53%) of the hepatitis delta virus RNA-negative subjects. Regarding hepatitis B virus DNA in serum and peripheral blood mononuclear cell, 71% (5 of 7) of the patients with serum hepatitis B virus DNA had this marker in peripheral blood mononuclear cell, whereas 52% (12 of 23) of the patients without serum hepatitis B virus DNA had hepatitis B virus DNA in peripheral blood mononuclear cell. A Southern blot analysis was also carried out on peripheral blood mononuclear cell samples from 30 patients. Hepatitis B virus DNA was detected in 16 patients as free forms, in 12 patients as dimers and free forms and as free circular together with free linear forms in the remaining two patients. 