Measurement of the area of the tumour deposits present in routine sections from the axillary nodes from a series of 1069 breast cancer patients showed that 138 cases had a single micrometastasis (0.2 cm2 or less), while in 29 a similar load was spread over two or more nodes. These 167 cases represent 15% of the patients in the series. Twentyfive of them had died of breast cancer within a mean follow-up of 6 years. They had smaller micrometastases than those surviving (P < 0.0025). Histological examination in the 138 with single micrometastases showed that two variants were present. In one, tumour growth was confined to the capsular lymphatics and/or the subcapsular sinus. In the other, tumour growth was present in the nodal lymphoid tissue, and, on occasion, at the other sites as well. Those with growth in the lymphoid tissue had a better prognosis than those without (P < 0.0035). Prognosis in the former was comparable to that in the node-negative cases, while in those lacking such growth it was similar to that in the node-positive. The presence of these two variants could explain divergent reports in the literature on prognosis in cases with micrometastases. While the mechanisms behind this apparent paradox remain speculative, the observation can be of diagnostic interest in routine surgical pathology.