To analyze the expression of bone morphogenetic proteins (BMPs) in prostate and breast cancers with established metastasis in bone, where prostate cancer causes osteoblastic metastases, and breast cancer osteolytic metastases.Primary tumor specimens from 20 patients with prostate cancer and 15 with breast cancer were studied for BMP-2/4, -3, -5, -6 and -7 immunohistochemistry. All patients had multiple bone metastases proven by bone scan. We also examined BMPs expression in normal prostate and breast tissues. BMPs expression was compared with clinicopathological and biochemical parameters.Cytoplasmic BMPs immunostaining was observed in both prostate cancer and normal prostate tissue. Expression of BMP-2/4, -5, -6, and -7 proteins was detected in all normal prostate samples, with the predominance of BMP-2/4 (87.8-/+11.4% positive cells) and BMP-7 (94.6-/+0.9% positive cells). In prostate cancer tissues, we found variable expression of all BMPs. BMP-2/4 (83-/+11.6% positive cells) was predominantly expressed in prostate carcinoma, whereas the expression of BMP-7 (24.3-/+19.2% positive cells) was significantly lower than in the normal prostate. In all breast cancers tissues, we found nuclear staining only for BMP-7. In normal breast tissue, the BMP expression was not detectable. The percent of BMP-7 positive cells in breast cancer (86.4-/+7.3%) was higher than in prostatic cancer. Comparing BMP expression levels and clinicopathological parameters, we did not find statistical difference, except for serum alkaline phosphatase, which was significantly higher in patients with prostate cancer.The expression of BMPs differs between prostate and breast cancer cells. Identifying the BMP proteins in cancers may be useful for monitoring the tumor status with reference to metastases.