Epidermal growth factor receptor was determined in 106 newly diagnosed breast cancer patients, using the biochemical method. The group consisted of 58 patients in stage I-II, and 48 patients in stage III-IV. Although a significant inverse correlation was found between EGF-R status, and ER or PR status, quantitative content of EGF-R did not correlate either with quantitative ER, or PR levels. The ER/PR content was similar in all clinical stages, suggesting their stability during the clinical course of the disease. EGF-R content was significantly higher in stage IV, compared to stage I, while intermediate clinical stages and all substages did not differ according to the EGF-R content. EGF-R was confirmed as a weak prognostic factor within clinical stages. However, in a whole group, the overall survival was significantly better in patients whose tumors EGF-R content was lower than 26 fmol/mg, compared to those with higher ERF-R content. EGF-R content was highly predictive for the response to systemic endocrine treatment, in metastatic breast cancer patients. In locally advanced breast cancer a trend towards higher levels of EGF-R was found in inflammatory breast cancers, compared to non-inflammatory ones. Slightly higher levels were found in responders to local non-endocrine primary treatments (radiotherapy with or without chemotherapy), compared to non-responders, suggesting the possible predictive role of EGF-R for the response to such treatments. Our results emphasized the usefulness of quantitative receptor determination suggesting the relative stability of EGF-R content during the clinical course of breast cancer, its independence from ER, its significant predictive and weak prognostic values, and a possible correlation with the aggressiveness of the disease, and response to non-endocrine treatments.