Abstract: The vitamin K epoxide reductase subunit 1 (VKORC1) has been identified recently. It is a component of the enzyme vitamin K epoxide reductase that is the therapeutic target site of warfarin. In order to investigate the relationship between VKORC1 gene and warfarin dose response, we studied this gene in an Iranian warfarin resistant patient who receive more than 100 mg warfarin per day. The results showed that although warfarin concentration in his plasma was extremely higher than therapeutic level (22.8 mg L-1) but no mutation(s) found in the exons of VKORC1 gene. Other genes may be contributed in resistance to warfarin in this patient.