PURPOSE: Gastric cancer cells may show resistance to various chemotherapeutic agents. The ability of cancer cells to become drug resistant is thought to be a cause of chemotherapy failure. Recent studies showed that multidrug resistance-associated protein (MRP) might confer resistance to a wide spectrum of natural product drugs. However, the clinical relevance of MRP-mediated multidrug resistance in human gastric cancer remains unknown. To determine the significance of MRP expression in gastric cancer, we investigated the relationship between MRP expression and chemosensitivity in gastric cancer cell lines. METHODS: In 8 gastric cancer cell lines (SNU-1, 5, 16, 484, 601, 620, 638 and 668), the expression of MRP and MRP mRNA was detected by using Western blot and reverse transcription-polymerase chain reaction (RT-PCR) analyses, respectively. Sensitivity to the anticancer agents (cisplatin, doxorubicin, 5-fluorouracil, camptothecin, epirubicin, and vincristine) was examined using a dimethylthiazole- diphenyltetrazolium-bromide (MTT) assay. RESULTS: All 8 cell lines expressed MRP and MRP mRNA in various degrees. There was no significant correlation between the expression of MRP and MRP mRNA. Sensitivity to anticancer agents had no significant correlation with the level of MRP expression. CONCLUSION: There was no general correlation between the expression of MRP and chemosensitivity in the various gastric cancer cell lines used in this study. In addition to MRP, another mechanism might be involved in the chemosensitivity of gastric cancer cell lines.