We examined CK19 mRNA expression in the peripheral blood mononuclear cells (PBMC) from patients with ovarian tumor by reverse transcriptase-polymerase chain reaction (RT-PCR) using primers which did not cross-amplify pseudogenes of CK19 gene. The incidence of positive CK19 mRNA expression in healthy individuals, benign ovarian tumor patients and ovarian cancer patients were 60% (12/20), 71% (10/14) and 84% (21/25), respectively. Although the frequency of positive CK19 mRNA expression in PBMC from ovarian tumor patients was higher than that from healthy individuals, there was no statistically significant difference between the frequencies. Moreover, one healthy control showed CK19 mRNA expression only in her menstrual period, not in her proliferative phase or secretory phase. These results suggested that CK19 is not a suitable target to detect the presence of tumor cells in the PBMC from patients with ovarian tumors.