The follow-up bone scans (BS) of 158 women with breast cancer and without known bone metastases were reviewed and compared with serum CA 15-3 concentration. Ninety-three BS were systematic (normal serum CA 15-3) and 3 corresponded to proven bone metastases. Sixty-five BS were motivated:-by isolated bone pain (20 BS. 1 corresponding to metastases),-by bone pain and signs of progression of the disease (11 BS. 7 corresponding to metastases: elevated serum CA 15-3 except in one case), by known visceral metastases (20 BS. 6 corresponding to metastases with elevated serum CA 15-3), by an isolated increase of serum CA 15-3 (7 BS. 4 corresponding to metastasis) by local recurrence (7 BS. 1 corresponding to metastasis). These results show that bone metastases were diagnosed in 6 patients whose serum CA 15-3 concentration was normal. We conclude that the existence of normal tumor markers is not sufficient to exclude the possibility of bone metastases.