We have measured the plasma PIVKA-II levels in 188 cases of various liver disease with HCC and malignant diseases in other organs by an EIA, using a monoclonal antibody (E-1023 kit, Eisai), and also have measured the plasma vitamin K levels in cases of HCC and cholestasis by an HPLC. Plasma PIVKA-II was detected in many cases of HCC (67%, 35 of 52 cases) and cholestasis (60%, 6 of 10 cases). In contrast, the positivities of PIVKA-II in the other diseases including benign liver diseases were very low. Combination assays of PIVKA-II and vitamin K revealed that PIVKA-II correlates with vitamin K in cholestasis but not in HCC, suggesting that PIVKA-II in HCC does not depend on a systemic deficiency of vitamin K. From these results, it was concluded that PIVKA-II is a reliable marker which can reflect the clinical course of HCC.