It has been shown that the level of estrogen receptors (ER), and to some extent progesterone receptors (PR), correlate to a high degree to the response to endocrine therapy in advanced breast cancer patients. To evaluate the prognostic value of ER/PR in early breast cancer, 80 patients with stages I and II were studied. They all underwent modified radical mastectomy. Patients with stage I disease (negative LN) received no further treatment, while those with stage II received standard adjuvant chemotherapy. All the patients were followed for 4 years. The ER and PR were measured in each primary tumor by the glycerol density gradient method. Values of 10 fmole/mgm protein or greater were considered positive (+) and less than 10 fmole/mgm were considered negative (-). The results revealed: (1) Fifty-two patients (65%) had ER+, of which 44 (85%) were also PR+; 28 patients had ER-, of which 24 were also PR- (p less than 0.0001). (2) ER/PR correlated with age as 71% of the patients over age 50 had ER+/PR+, compared to 33% of those under age 50 (p less than 0.05). (3) Postmenopausal patients had a higher incidence of ER+/PR+. (4) Primary tumors less than 2 cm in size had higher ER+; 71% in those with stage I and 80% in stage II. (5) Fifty-eight per cent (38) of patients with ductal carcinoma had ER+/PR+, compared to 67% (4) with lobular carcinoma. (6) The disease-free survival of patients with ER+ tumors was significantly longer than those with ER- tumors (p less than 0.005) both in positive and negative LN patients. The same was true for PR+ compared to PR- (p less than 0.005), but only in those with stage II disease. The overall survival rates were similarly significant in favor of ER+ and PR+ patients (p less than 0.025), but only in stage II disease. It seems that the status of steroid hormone receptors has a major prognostic factor second only to the LN status.