Estrogen (ER) and progesterone (PR) receptors were assayed in the center and the periphery of 24 primary breast cancers and correlated with seven morphological features of the tumors. Quantitative variations in ER and PR contents between center and periphery were not significant, and the major discordance rate of the receptor status was only 8.3% for ER and 12.5% for PR. Among all morphological features studied, only tumor cellularity was correlated with steroid receptors; thus 18 out of 19 ER-positive samples (p less than 0.005) and 15 out of 16 PR-positive samples (p less than 0.025) were tumor cellularity 2-3, and higher ER (p less than 0.003) and PR (p less than 0.007) levels were found in tumor cellularity 2-3. Our results indicate that steroid receptors should be assayed in samples with a high content of tumor cellularity, whether the sample is taken from the center or the periphery of the tumor.