To evaluate the role of serum alpha-L-fucosidase (AFU) in the diagnosis of hepatocellular carcinoma (HCC), we simultaneously studied both AFU activity and alpha-fetoprotein (AFP) level in 60 patients with HCC, 60 patients with cirrhosis and chronic hepatitis each, 30 patients with other liver tumors and 60 healthy subjects. Serum AFU activity in patients with HCC (1,418.62 +/- 575.76 nmol/ml/hr) was significantly higher than that found in cirrhosis (831.25 +/- 261.13 nmol/ml/hr), chronic hepatitis (717.71 +/- 205.86 nmol/ ml/hr) or other tumors (706.68 +/- 197.67 nmol/ml/hr) and in controls (504.18 +/- 121.88 nmol/ml/hr, p < 0.05). With 870 nmol/ml/hr (mean value of controls plus 3 standard deviations) considered as the cut-off point, AFU was more sensitive (81.7 vs 39.1%) but less specific (70.7 vs 99.3%) than AFP at a level of > 400 ng/ml as a tumor marker of HCC. With both markers combined, the sensitivity was improved to as much as 82.6%. AFU activity in HCC patients was correlated to tumor size (r = 0.3529, p = 0.006) but not associated with tumor staging classified by Okuda's criteria (p = 0.1). The AFU activity in the viral hepatitis group (hepatitis B or C) was also significantly higher than in the non-viral group (p = 0.0005). We conclude AFU to be a useful marker, in conjunction with AFP and ultrasonography, for detecting HCC, particularly in patients with underlying viral hepatitis and cirrhosis.