The purpose of our study was to clarify whether the amount of tissue extracted by means of iliac crest needle biopsy (ICNB) would suffice for a quantitative determination of estrogen receptors (ER) in bone metastases, and to see if the method currently used for determining ER in primary tumors could also be successfully utilized in ICNB. 22 of 31 breast cancer patients examined could be evaluated. ER was positive in 7 (31.8%). Reasonable data are to be expected when the biopsy weight exceeds 0.1 g. Our study confirms that the necessary amount of tissue for ER analysis can indeed be extracted by ICNB. Our results justify further studies on a larger group of patients, since we cannot make conclusive statements concerning the value of this method for predicting the ultimate success of an endocrine treatment.