['To determine whether PIVKA-II can serve as a monitoring marker of warfarin treatment.', 'The correlation between PIVKA-II concentration and INR was analyzed among outpatients on warfarin therapy and PIVKA-II concentration after commencement of warfarin administration was monitored for six patients.', 'PIVKA-II concentration and INR were significantly correlated in the patients on regular warfarin therapy. PIVKA-II level increased abruptly after start of warfarin administration.'] Is pIVKA-II a candidate marker for monitoring the effects of the oral anticoagulant warfarin?