OBJECTIVE To investigate the value of the determination of the levels of serum argininosuccinate lyase (ASL) in diagnosing various liver diseases. METHODS Two hundred and ninety-one patients with various liver diseases, 257 patients with non-liver disease, and 32 healthy controls were recruited for this study and their serum ASL, ALT, AST, GGT, LDH, ALP, and total bilirubin (TBil) levels were determined. Liver biopsies were performed on 31 patients with hepatopathy. RESULTS Receiver operating characteristic (ROC) curve analysis showed that the sensitivity and specificity of ASL in assessing liver diseases were 100% and 91.1% (at cut-off values of 8 U/L), those of ALT were 97.6% and 24.7% and those of AST were 83.8% and 28.3% (both at cut-off values = 40.0 U/L), respectively. The levels of ASL in various liver disease patients were: in liver cancer - acute hepatitis - liver cirrhosis - chronic hepatitis. A positive correlation (r = 0.417) was observed between serum ASL levels (86.9+/-26.5) and scores of histopathological inflammation grading (9.83+/-3.36). CONCLUSIONS ASL is of higher sensitivity and specificity than those of ALT and AST for diagnosing liver diseases. ASL may be used as a useful marker in estimating hepatopathy.