Blood hyaluronic acid (HA) concentration was measured in dogs with various liver diseases to determine its relationship with histological fibrosis of the liver. The blood HA concentration significantly increased in dogs with chronic liver diseases compared with extrahepatic diseases and control. Furthermore, the median blood HA concentration in dogs with liver cirrhosis (500 microg/l; range, 151-1970 microg/l) was significantly higher than dogs with non-cirrhotic liver diseases (153 microg/l; range, 15-477 microg/l). In histochemical analysis, HA was distributed primarily in the fibrotic area in dogs with chronic liver diseases. As a conclusion, the blood HA concentration was significantly increased in dogs with chronic liver diseases, especially those with cirrhosis. Measurement of the blood HA levels of dogs with suspected liver disease can be a useful diagnostic aid for canine cirrhosis.