To clarify the relationship between multidrug resistance protein (MRP) and clinicopathologic features, the influence of adjuvant chemotherapy, and prognosis of patients who underwent resection of metastatic liver carcinomas originating from colorectal carcinomas, we examined the expression of MRP in tumor tissues by immunostaining. Specimens of 38 primary colorectal tumors and 44 metastatic liver tumors of colorectal origin were examined (metastatic group). We also examined 28 nonmetastatic colorectal carcinomas. The percentages of nonmetastatic tumors and of primary and metastatic tumors of the metastasis group that expressed MRP were similar. MRP expression in primary and metastatic tumors did not correlate with any clinicopathologic features. The use of adjuvant chemotherapy after operation for primary colorectal carcinomas was associated with increased MRP expression among metastatic liver tumors. Expression of MRP in the tumor did not influence the prognosis or survival rate after resection of primary or metastatic tumors. Our data suggest that MRP expression in metachronous liver metastases from colorectal carcinomas may be induced by administration of anticancer drugs but is not associated with clinicopathologic features of the tumor, liver metastasis, or prognosis.