The axillary lymph nodes of 100 lymph node-negative breast cancer patients with known bone marrow status have been re-examined to explore the presence of micrometastasis in lymph nodes and the covariance of micrometastasis to bone marrow and lymph nodes. Nodes were serially sectioned at three intervals of 100 microm, followed by immunohistological (two sections) and haematoxylin-eosin staining (one section). Tumours were mainly T1 and T2, and the patients had on average 13 (4-22) lymph nodes removed. In two patients, micrometastasis was detected in one node. Another 25 patients possessed single positive immunostained cells mimicking tumour cells. These cells have been shown to be false positive cells by Perl and melanin staining. One patient had metastasis to several nodes missed by the original examination. Immunocytochemical detection of micrometastasis in bone marrow revealed 11 marrow-positive patients. This study has identified a low frequency of micrometastasis to lymph nodes, and no covariance with micrometastasis in the bone marrow was seen. Bone marrow micrometastasis may be an independent prognostic variable, separate from axillary node status.