We have studied the clinical value of immunohistochemical techniques in detecting occult axillary metastases from breast carcinoma in forty patients, all of whom had been assessed as free of nodal metastases by routine histology 5 years earlier. The same sections were restained using monoclonal antibodies against Epithelial Membrane Antigen (EMA). In four patients, occult metastases were detected, giving an increase in diagnostic accuracy of 10%. At 5-year follow-up 12 (30%) patients had developed tumour recurrence, of whom three were detected on immunohistochemical testing, while the other nine patients were reported as free of nodal metastases on staining with Anti-EMA. We conclude that routine application of immunohistochemical staining would further increase the diagnostic yield of axillary metastases from breast carcinoma, but this increase would not be of significant clinical value.