We evaluated the correlation between hepatitis B surface antigen (HBsAg) and a serum fibrotic marker, the procollagen type III N-terminal peptide (PIIINP), levels, an indicator of synthesis and degradation of type III collagen, among patients with chronic hepatitis B virus (CHB) infection. Eighty-four patients with chronic HBV infection without previous antiviral treatment were recruited into the study. There were 58 males and 26 females and the median age was 40 years old. The patients were divided into 3 groups of 28 patients each by stage of chronic HBV infection. PIIINP levels and HBsAg titers were determined by ELISA for all the subjects. The mean overall HBsAg titer correlated significantly with the mean PIIINP level (r = 0.548; p < 0.01). The correlation between the mean HBsAg titer and the mean PIIINP level in the low replicative phase group (r = 0.808) was significantly greater than in the other 2 groups (p < 0.01). The PIIINP level may be a disease activity parameter, especially during the low replicative phase of chronic HBV infection.