Objectives To determine whether the urinary excretion of urinary pyridinoline (Py) and deoxypyridinoline (dPy) serve as markers to evaluate the activity of bone metastases and the response to endocrine therapy, by determining the relationship between the excretion of these compounds and the activity of bone metastases in patients with prostate cancer. Patients and methods Urine specimens were obtained from 15 patients with benign prostatic hypertrophy (BPH), 17 with carcinoma clinically confined to the prostate and 26 with prostate cancer and bone metastases. Among the patients with prostate cancer and bone metastases, 15 were new or reactivated cases and the 11 others were well controlled by hormonal therapy. Urinary Py and dPy were analysed using high‐pressure liquid chromatography. Results Patient with new or reactivated prostate cancer with bone metastases had a higher urinary excretion of Py and dPy than did the patients with BPH, patients with prostate cancer and no bone metastases and patients with prostate cancer and bone metastases well controlled with hormonal therapy. Urinary levels of these compounds correlated with the extent of bone metastases in new and reactivated cases. Initial high levels of these cross‐linked compounds in patients with multiple bone metastases fell as the prostate cancer was controlled by hormonal therapy. Conclusion Urinary excretion of Py and Dpy appears to be a useful marker for evaluating the activity of bone metastases and their response to hormonal treatment in prostate cancer.