Bone marrow scintigraphy was performed in 23 patients with histologically proven carcinoma of the prostate, using a new radiopharmaceutical, Technetium-99m nanocolloid. The results suggest that although bone marrow scintigraphy is less sensitive than conventional bone scintigraphy in the detection of skeletal metastases from prostatic carcinoma, the technique may have a place in the management of patients with advanced metastatic disease, especially those who are anaemic, by identifying those patients at risk from myelosuppressive therapy.