Recent evaluation of human prostate tissues has shown predominantly high expression of the macrophage colony-stimulating factor receptor in prostatic intra-epithelial neoplasia or prostate cancer. However, the expression of its ligand, the macrophage colony-stimulating factor (M-CSF), and the biological role of this signaling in prostate cancer has not been analyzed. In this research we determined the relationship of serum M-CSF level to clinical parameters of prostate cancer progression. We measured the serum level of M-CSF in 170 patients with histologically confirmed prostatic adenocarcinoma and in 54 patients in whom prostate cancer was not detected. We also investigated the M-CSF expression in prostate cancer tissues by immunohistochemistry. The serum levels of M-CSF in bone metastatic prostate cancer patients was significantly higher than those in non-metastatic patients, while M-CSF did not differ with regards to histological grade, Gleason score or local tumor progression. M-CSF expression was detected in prostate cancer cells themselves by immunohistochemistry. These results suggest that M-CSF may have a functional role in prostate cancer progression.