Objective To explore the significance of using cytologic and RT-PCR methods to examine(peritoneal) washings and peritoneal tissues of gastric cancer patients in prediction of peritoneal micrometastasis.Methods The peritoneal washings of 38 patients with gastric cancer and 5 patients with benign gastric(lesions) were collected and,at the same time,a small amount of omentum and peritoneum were removed for control.CEAmRNA expression of free cells in peritoneal washings were detected by RT-PCR method and(also) cytology of the washings were performed.Results The CEAmRNA expression rate of peritoneal washings and peritoneal tissues were 36.8%(14/38) and 39.5%(15/38)respectively.Both were more(sensitive) than that of cytologic examination 26.3%(10/38).TNM staging,depth of invasion,lymph node metastasis,and serosal involvement were related to the expression rate of CEAmRNA.Conclusions mRNA of CEA is more sensitive and specific than cytologic examination for detecting free cancer cells in peritoneal cavity.It is an effective method for detecting peritoneal micrometastases in gastric cancer patient.