BACKGROUND: The serum des-gamma-carboxy prothrombin (PIVKA-II) is a tumor marker complementary to alpha-fetoprotein (AFP) for diagnosing primary hepatocellular carcinoma (HCC). A combination assay of the tumor markers was found to be useful for early diagnosis of HCC. So we investigated the clinical relevance of the measurement of serum PIVKA-II and AFP levels in patients with HCC. METHODS: The serum PIVKA-II levels were measured in 64 cases of HCC, 16 cases of cirrhosis, 32 cases of chronic hepatitis, and 23 healthy controls with a revised PIVKA-II ELISA Kit (Eisai, Tokyo, Japan), with the simultaneous determination of the serum AFP value using the AFP immunoassay kit (Elecsys, Roche, Germany). RESULTS: The positive rates of PIVKA-II and the AFP value in HCC were 53.1% and 68.8%, respectively, and were significantly higher than 17.6% and 29.4% in liver cirrhosis, and 3.1% and 0% in chronic hepatitis. No signficant correlation between the two tumor markers was found. The correlation between PIVKA-II levels and the size of tumor in HCC was found. No relation of the clinical characteristics to positive rates of PIVKA-II and AFP was found. The sensitivity, specificity and accuracy of PIVKA-II were 53.1%, 94.4% and 73.8%, and those of AFP were 68.8%, 93.1% and 80.9%, respectively. The sensitivity and accuracy in the combination assay for detection of HCC were higher than those in each assay, especially in HCC with the diameter of the tumor mass at less than 3 cm. CONCLUSIONS: It was demonstrated that the combination assay of PIVKA-II and AFP could increase the diagnostic value for HCC and could be useful in early diagnosis of HCC.