Analysis of 104 breast cancer biopsies (removed prior to any treatment with tamoxifen or chemotherapeutic agents) from patients aged between 31 years and 89 years at the time of diagnosis (mean age = 58 years). Twenty were less than 50 years and seventy-seven women were 50 years, or older, at diagnosis. The size of the tumours ranged between 0.6 cm and 8.0 cm (mean = 2.79 cm). Eighteen tumours were T1 (<2 cm) in maximal dimension; 83 were T2 (25 cm) and 3 tumours were T3 (>5 cm). Eighty-two were invasive ductal carcinoma, 17 were invasive lobular and five were tumours of special type (two tubular and three mucinous). Eleven tumours were grade 1; 40 were grade 2; and 53 were grade 3. Sixty-seven tumours were oestrogen receptor (ER) positive and 34 were ER negative (ER status was determined by Enzyme Immuno-Assay (EIA); a positive result was defined as more than 200 fmol/g protein). ER status was not available for 3 patients. Forty-five tumours had no axillary metastases and 59 tumours had metastasised to axillary lymph nodes. Sixty-nine women were treated with post-operative tamoxifen; 26 did not receive tamoxifen. Fifty patients were treated with adjuvant systemic chemotherapy (CMF +/ adriamycin); 45 patients did not receive chemotherapy. Details regarding tamoxifen and systemic chemotherapy were not available for 9 patients. Maximal follow-up was 3,026 days with a mean follow-up of 1,887 days.