The assessment of steroid hormone receptors in resected breast cancer tissues is essential to decide whether endocrine therapy is indicated and to select the best treatment for each patient on the basis of receptor status. Both enzyme immunoassay (EIA) and immunohistochemistry (IHC) have been generally used as methods for examination of estrogen receptor (ER) and progesterone receptor (PgR). In some patients, receptor status cannot be examined for various reasons. A questionnaire survey in Japan clarified that ER status is not examined in approximately 40% of patients receiving breast conserving surgery. To eliminate "receptor unknown" cases, IHC examination on paraffin-embedded tissue is useful to assess the in situ receptor status. The concordance rate of ER and PgR status between EIA and IHC is very high and a study of 88 cases revealed a 97.7% concordance for ER and 92.0% for PgR at a cutoff point of 10%. The cutoff point of IHC is controversial and some studies demonstrated that patients showing 1% ER positive cancer cells would benefit from endocrine therapy. On the other hand, immunohistochemical expression of receptors is heterogeneous and some patients with ER negative invasive tumors have ER positive intraductal components. A study of 65 breast cancers demonstrated that ER positive intraductal components were detected in 3.1% cases of ER negative invasive lesions. According to these results and the recommendation of the St. Gallen International Conference, IHC is thought to be more useful than EIA in the assessment of steroid hormone receptor status for breast cancer patients.