Bone marrow is a prognostically relevant indicator organ for micrometastasis. In the present study, real time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect disseminated gastric cancer cells in bone marrow. We compared CEA, CK18 and CK20 expression using four gastric cancer cell lines and three normal tissue cell lines in order to select the most appropriate marker for detection of disseminated gastric cancer cell in bone marrow. CK20 proved to be the most promising marker since the expression level of normal cell lines was extremely low and about 50--100-fold differences were found between gastric carcinoma cell lines and normal tissue cell lines. We also screened bone-marrow RNA of 47 patients with gastric cancers, using this system. Among the three markers we tested, with only about CK20 could we find that 27 of 47 patients were positive. Though long-term clinical follow up studies are needed to evaluate the clinical significance of this method, real time quantitative RT-PCR is sensitive and quantitative for detection of micrometastasis in bone marrow.