We describe a simple and sensitive method for detection of low number of cancer cells in the blood. The method is based on FACS sorting of leukocytes labelled with anti-CD45 monoclonal antibody and examining CD45- cells by conventional cytology and immunostaining for cytokeratin 18. In a model study, cancer cells seeded at the frequency of 1 per 106 and 1 per 107 leukocytes were detected in CD45- population. Sensitivity of this method was comparable to reverse transcription polymerase chain reaction (RT-PCR) used for detection of cancer cells expressing CD44 variants-mRNA. In a pilot study, cancer cells were also isolated from the blood of some patients with locally advanced gastric cancer. This method may be useful for detection of circulating tumour cells in cancer patients.