The cytosolic estrogen receptor (CER) content of 1037 primary breast carcinomas was evaluated by sucrose density gradient analysis. Tumor specimens from premenopausal patients had significantly lower levels of CER (14.6 +/- 1.5 (mean +/- SEM) 8S binding fmole/mg protein) compared with carcinomas from postmenopausal patients (57.5 +/- 3.9 fmole/mg protein; p less than 0.001). The proportion of specimens with CER levels above threshold values of 3, 7, or 10 fmoles/mg protein were significantly higher for postmenopausal patients (72%, 63%, 59%, respectively) than for premenopausal patients (56%, 42%, 36%, p less than 0.001). When compared within half-decades, no statistically significant differences between premenopausal and postmenopausal patients were observed for mean, median, or rank sums of CER levels (p greater than 0.3). When patients were compared by half-decades, both mean and ranked sums of CER levels were significantly different (p less than 0.001). The proportion of specimens that demonstrated CER levels above a threshold value of 10 fmole/mg protein increased sequentially from a low of 13/51 (26%) for patients less than 35 years to a high of 60/81 (74%) for patients greater than 75 years.