Response of breast carcinomas to tamoxifen treatment depends, among others, on the estrogen receptor status. The estrogen receptor content was semiquantitatively determined in immunostained sections of stage 1 and 2 cancers of patients who had undergone tumor excision, tamoxifen treatment, adjuvant chemotherapy and radiotherapy. Weighted scores of the estrogen receptor content of the tumors were established by calculating the arithmetic means of the intensity of stained nuclei and the number of positively stained nuclei. Statistically, a cut-off value of > or = 2.1 signified a good prognosis; all patients whose tumors disclosed a weighted score of > or = 2.1 were alive and free of disease at the 10-year postoperative follow-up examination. On the other hand, one third of the patients whose carcinomas had a weighted score of < 2.1 presented with locally recurrent cancer, distant metastases, or both during the follow-up observation period. The statistically significant association between the patients' 10-year event-free survival and carcinomas with a weighted score of > or = 2.1 may serve oncologists in their decision making with respect to hormonal treatment.