Hepatitis delta virus (HDV) RNA detection was carried out, using a full-length HDV RNA probe, in serum of 43 patients with chronic HDV infection. Among them, 30 cases (70%) were HDV RNA-positive. With respect to other HDV markers, serum HDAg (detected by immunoblot) was found in 33 patients (77%) and IgM anti-HD in 29 (67%). A similar percentage of HDV RNA-positive patients with and without circulating hepatitis B virus (HBV) DNA (32.5 vs. 37%, respectively) was found. Antibodies against the human immunodeficiency virus (HIV) were detected in 15/43 subjects studied. The presence of HDV RNA was significantly higher (p