This study evaluates the role of reverse-transcriptase polymerase chain reaction (RT-PCR) assay for carcinoembryonic antigen (CEA), cytokeratin 19 (CK19), and maspin transcripts to identify breast cancer cells (BCC) in leukapheresis products (LP) collected from breast cancer (BC) patients and compares these results with those obtained using immunocytochemistry (IC). Eighty-four LP obtained from 33 patients with stage II-III BC and control subjects without BC were screened for the presence of BCC by IC and CK19, CEA, and maspin expression using RT-PCR. CEA RT-PCR and IC were the only specific markers, as no false positives were detected in any patients without BC. CK19 RT-PCR gave 11% false positives, whereas maspin RT-PCR with 25% was the most unspecific marker. In LP from BC patients, positive results were observed in 70% and 63% for CK19 and CEA RT-PCR, respectively. For maspin RT-PCR, this percentage was 22%, and for IC it was 17%. There was a good correlation between the CEA and CK19 RT-PCR (p = 0.018). No correlation between CEA and CK19 RT-PCR and IC was found, and although 5 of the 6 IC+ samples were CEA+/CK19+, great discrepancies in the group of IC- samples were observed. Our data suggest that RT-PCR assays for CEA and, to a lesser extent, for CK19 have more sensitivity and specificity than IC to detect BCC in LP.