In order to examine the clinical significance of the tamoxifen binding site, correlations between the concentration of the tamoxifen binding site and either the estrogen receptor (ER) or progesterone receptor (PgR) were studied. A saturable high-affinity tamoxifen binding site was detected in human breast cancer tissues. The concentration of the tamoxifen binding sites in 12,000 g supernatant of ER positive tumors was 122.3 +/- 186.8 (mean +/- SD) fmol/mg protein, and that of ER negative tumors was 68.38 +/- 82.97 fmol/mg protein. The concentration of the tamoxifen binding sites in 12,000 g supernatant of PgR positive tumors was 103.7 +/- 137.3 fmol/mg protein, and that in the 12,000 g supernatant of PgR negative tumors was 90.29 +/- 159.0 fmol/mg protein. There was no significant difference between the concentration of the tamoxifen binding sites in the 12,000 g supernatant of ER positive tumors and ER negative tumors, and there was no significant difference between the concentration of the tamoxifen binding sites in the 12,000 g supernatant of PgR positive tumors and PgR negative tumors. The concentration of the tamoxifen binding sites in the cytosol of PgR positive tumors was 90.55 +/- 103.5 fmol/mg protein, and that in the cytosol of PgR negative tumors was 29.13 +/- 42.22 fmol/mg protein. There was a significant difference between them (p less than 0.05). The concentration of tamoxifen binding sites in 12,000 g supernatant had no correlation with the values of ER and PgR. Only the content of tamoxifen binding sites in cytosol, and the PgR value had a significant correlation.(ABSTRACT TRUNCATED AT 250 WORDS)