Random bone marrow biopsies were examined in 28 patients with proven carcinoma of the prostate. In 6 cases (28-5%) bony metastases were demonstrated and in 2 of these X-ray skeletal surveys were negative. It is suggested that bone marrow biopsy should be done in the staging of carcinoma of the prostate when other investigations are negative, especially when an occult primary is suspected, when radical treatment is contemplated and in clinical trials.