With immunohistochemical technique, epithelial membrane antigen monoclonal antibody (EMA) has been used to detect the micrometastatic focus in bone marrow of patients with primary gastric cancer since 1992. In the exmamination of 65 patients, the positive rate of bone metastasis was 58.46%. After comprehensive treatment to these patients, comparative observation showed that there were marked differences between pre-therapeutic (9.45) and post-therapeutic (2.19). The result demonstrates that this technique provides identification of blood micrometastases and has insttructive signnificance for clinical comprehensive treatment.