The molecular species of hepatitis B virus (HBV)-DNA of 44 sera taken from 25 HBV carriers were examined by Southern blot hybridization with a biotin-labeled HBV-DNA probe and classified into three patterns. Type I consisted of two distinct bands of 4.0 kb and 3.2 kb. Type II consisted of the 4.0 kb and 3.2 kb bands and a smear between these two bands. Type III showed a broad band below 4.0 kb. With endogenous HBV-DNA polymerase reaction, the smear disappeared and 4.0 kb and 3.2 kb bands appeared. After EcoRI digestion, the 4.0 kb band disappeared to form a single band of 3.2 kb. These results suggest that the 4.0 kb and 3.2 kb forms are a relaxed circular, fully double-stranded DNA and a linear, fully double-stranded DNA, respectively, and that the smear between 4.0 kb and 3.2 kb is formed from the sum of relaxed circular, partially double-stranded DNAs with various length of plus strands. Comparison between histological diagnosis and Southern blot hybridization patterns of 25 HBV carriers indicates that these three patterns are closely related to the degree of hepatitis.