The oestrogen receptor (RE) status of the primary tumour has been assessed in 466 of a consecutive series of 550 patients with primary operable breast cancer. All patients were followed up (without treatment) until the development of recurrence or metastases. Distant metastases have so far occurred in 124 patients and 82 have had symptomatic local or regional recurrence. A significant correlation exists between the RE status of the primary tumour and subsequent patterns of metastasis. Symptomatic metastases to regional lymph nodes are more common with RE- cancers. There is no significant difference in either time of onset or total incidence of distant metastases between patients with RE+ and RE- tumours. Distribution of distant metastases is influenced by RE status: RE+ tumours tend to recur in bone, RE- tumours show affinity for viscera.