We investigated hepatitis B virus (HBV) DNA in liver samples from 22 patients with acute benign hepatitis (AH) and 26 with acute fulminant hepatitis (FH) and compared the results with those obtained by detection of serum HBV DNA and HBV serological markers. Free HBV DNA forms were detected in 11 patients with AH and one with FH, a reflection of active HBV DNA replication in three patients and the end of viral multiplication in nine. Free monomeric HBV DNA was present in three patients with AH and six with FH, and free oligomers were identified in three patients with AH. Results from two patients with AH and seven with FH suggested the presence of dimeric or multimeric HBV DNA. Thus, the various forms of HBV DNA previously described in chronic HBV carriers may be observed at the acute stage of the viral infection. After comparing serological and hybridization data, we found that nine of 19 patients (one with AH and eight with FH) lacking serum HBV surface antigen might have had acute hepatitis related to infection with HBV or HBV variants.