Recent studies have suggested that mRNA transcribed from cancer/testis genes might be used as biomarkers of cancer cells that migrate through the blood system. Using RT-PCR, we evaluated the expression of several cancer/testis mRNAs (MAGEA1-6, GAGE1-8, NY-ESO-1, SSX1, 2, and 4, XAGE1 and MAGE-C1) in primary tumors and peripheral-blood samples of colorectal cancer patients. The rate of detecting at least one of the transcripts was 95% (37/39 samples) for primary tumors and 81% (52/64 samples) for peripheral blood. Moreover, the selected mRNA was detectable in the cellular fraction of the peripheral blood at all stages of the disease (14 out of 14 cases), whereas, in the extracellular fraction of plasma, this mRNA was only found at stages III and IV. The obtained data represent the possibility of the early diagnosis of colorectal cancer in highrisk individuals via peripheral blood analysis.