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 <0.005) and 15 out of 16 PR-positive samples (p <0.025) were tumor cellularity 2–3, and higher ER (p <0.003) and PR (p <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 tu