Steroid hormone receptors for oestradiol (ER) and progesterone (PR) have been measured sequentially in primary and metastatic breast cancer to determine whether receptor status remains concordant in individual patients. Serial receptor measurements from the same tumor site showed a change from receptor-positive to receptor-negative tissue with time in some patients. Receptors were measured in primary tumor and later metastatic disease or tumor of the contralateral breast in 28 patients. Concordant results were found in 46% of cases. Six of nine patients with ER-positive primary tumors developed ER-negative metastases and four of five PR-positive primary tumors were associated with PR-negative secondary deposits. Nine of 19 patients with ER-negative primary tumors later had ER-positive metastases, and three of 15 PR-negative primary tumors were associated with PR-positive secondary deposits. Possible false-negative ER measurements (ER-, PR+) in primary tumors, and interval treatment with chemotherapy or hormonal manipulation between biopsies may have contributed to these changes in receptor status. Six patients changing from receptor-negative primary tumors to receptor-positive metastases underwent hormonal therapy of metastatic disease, and four had objective responses to treatment. Care should be taken when using receptor measurements from primary breast tumors to help decide treatment for later metastatic disease.