To clarify the correlation of hepatitis D virus (HDV) infection and viral replication in liver diseases, the authors detected HDV RNA and serological HDV markers in serum from 285 patients with hepatitis B and 45 asymptomatic carriers of HBsAg. With dot blot hybridization, serum HDV RNA was detected in 8.8% (29/330) of the patients with HBV infection. The positive rate of HDV RNA in fulminant hepatitis was higher than that in benign hepatitis (15/74 vs 3/47, P less than 0.05). 10 of the 139 patients with chronic active hepatitis and 1 of the 6 cases with cirrhosis were positive for HDV RNA. However, all of the 19 cases with chronic persistent hepatitis and 45 asymptomatic carriers of HBsAg were negative fo, HDV RNA. Serological HDV markers, HDAgr anti-HD and IgM-anti-HD, were determined with ELISA. HDV RNA was detected in all of the serum samples with positive HDAg and/or IgM-anti-HD, in 15 of the 26 cases with positive-anti-HD and in 8 cases without HDV markers. Our results showed that 40 of the 330 patients with HBsAg were infected by HDV. This investigation suggests that HDV is one of the etiological factors for fulminant hepatitis and chronic active hepatitis.