Background/Purpose: Hepatic fibrosis can progress in biliary atresia (BA) and is associated with capillarization of hepatic sinusoids. The significance of serum hyaluronic acid (HA) as a noninvasive indicator of histological sinusoidal endothelial cell (SEC) damage and hepatic fibrosis in BA, is investigated. Methods: A total of 28 postoperative BA patients (mean age, 11.0 +/- 3.7 years) and 20 normal controls (mean age, 10.5 +/- 2.8 years) were studied. BA patients were divided into group I, good liver function (n = 8); group II, moderate liver dysfunction (n = 10); and group III, severe liver dysfunction (n = 10). Serum HA was determined using a one-step sandwich enzyme immunoassay, and liver histological damage was confirmed immunohistochemically using an antibody against factor VIII-related antigen (FVIIIRAg), which is specific for detecting damaged SEC. Results: Serum HA was significantly higher (P < .0001) in group III (84.8 +/- 80.5 ng/mL) than in group 1 (15.9 +/- 6.9 ng/mL) or group 11 (28.7 +/- 10.7 ng/mL). Although immunoreactive products of FVIIIRAg were abundant in group III, they were not detected in SEC from group II. Conclusion: Serum HA may be of value for monitoring postoperative BA patients as a noninvasive indicator of SEC damage and progressive hepatic fibrosis. J Pediatr Surg 34:1791-1794. Copyright (C) 1999 by W.B. Saunders Company.