The serum level of N-terminal propeptide of collagen III (Col 1-3) has received increasing attention as a possible marker of liver fibrosis. Elevated levels have been reported in patients with primary biliary cirrhosis (PBC). We measured Col 1-3 levels in 24 patients with PBC (mean age 56 +/- 8 years) and compared their value as a prognostic marker with serum bilirubin and IgM levels, the aminopyrine demethylating capacity (ABT) and presence of clinical symptoms. Mean observation time was 5.1 +/- 2.7 years. When these parameters and age were evaluated as predictive factors for survival, only bilirubin, Col 1-3 levels and symptom status variables were found to be significant. When tested as explanatory variables for survival in a stepwise linear logistic regression model Col 1-3 was identified as the strongest significant (P less than 0.001) explanatory variable followed by bilirubin (P less than 0.01) whereas the symptom status emerged as a non-significant variable. The results suggest that the serum level of Col 1-3 may be a useful prognostic indicator in PBC, which is independent of the bilirubin level.