The extracellular matrix (ECM) is a complex of macromolecules that includes collagens, proteoglycans, and complex glycoproteins. In fibrotic liver tissue there is an increase in all of these matrix components, and they increase in serum in the patients with alcoholic hepatitis or liver cirrhosis. These ECM components have been used as a serum marker of hepatic fibrosis. Prolonged obstruction of bile flow results in morphologic and biochemical changes and the development of secondary biliary cirrhosis. In congenital biliary atresia (CBA) there is a close correlation between the degree of the hepatic fibrosis and bile flow after the operation. We estimated that, in CBA, ECM increased in serum, and it would reflect the degree of the hepatic fibrosis. To clarify this we examined the serum procollagen-III-peptide (P-III-P) and laminin in CBA patients. P-III-P was elevated in all preoperative patients but in two of the three postoperative patients whose jaundice disappeared P-III-P was in the normal range. In the all 3 patients whose jaundice continued, P-III-P was in normal range. Serum laminin was elevated in 12 preoperative patients with CBA, but there is no correlation between day of diagnosis and level of laminin. Mean concentration in CBA without jaundice after operation was 3.18 U/mL, 3.226 U/mL in CBA with jaundice and 3.3 U/mL in infantile hepatitis. There were no significant differences among three groups. With the elevation of serum alanine aminotransferase, aspartate aminotransferase, and total bilirubin, serum laminin level was also increased.(ABSTRACT TRUNCATED AT 250 WORDS)