The GA733-2 gene encodes the epithelial glycoprotein 40, a homophilic cell-cell adhesion molecule, which is expressed on the surface of epithelial cells and associated with a variety of carcinomas, e.g. breast, colorectal and lung carcinomas. To test if it could serve as a tumor marker, we have analysed the expression of GA733-2 in bone marrow (BM) and peripheral blood (PB) from healthy donors, and of patients with haematological malignancies or breast cancer using reverse transcriptase-polymerase chain reaction (RT-PCR). The GA733-2 nested PCR was positive in 100% (8/8) of BM and 40% (16/40) of PB from healthy donors, in 100% (33/33) of BM from patients with breast cancer who had no evidence of distant metastases and also in BM and PB from patients with haematological malignancies. GA733-2 mRNA is not specific as a marker for the detection of breast cancer cells in BM and PB.