The aim of this thesis was to use RT PCR to identify 3 putative breast cancer antigens or markers, cytokeratin 19 (CK 19), mucin 1 (MUC1) and carcinoembryonic antigen (CEA) in sentinel lymph nodes from breast cancer patients and compare the expression of these markers with each other and with conventional H&E histology of the sentinel nodes. In particular the technique was used and compared in half sentinel lymph nodes (group 1) versus 4μm sections cut from a different group of sentinel lymph nodes (group 2). There are no reports in the literature of the technique being used to evaluate different amounts of sentinel lymph node tissue. There was poor correlation between expression of the 3 different markers and between marker expression and H&E histology in both groups 1 and 2. Contrary to that expected, marker expression did not depend on the proportion of the lymph node examined by RT PCR although more lymph nodes were upstaged when more tissue was examined by RT PCR (group 1). In conclusion, even when the expression rates of CK19, MUC1 and CEA were considered together and when RT PCR was used to examine half the sentinel node, RT PCR was not sensitive enough to reliably detect metastatic disease in sentinel lymph nodes from these breast cancer patients. The technique is therefore not safe for clinical practice when applied to these three markers.