Radioactive phosphorus effected substantial palliation of intractable bone pain in 17 of 33 (51.5%) women with metastatic carcinoma of the breast and in 14 of 15 (93.3%) men with metastatic carcinoma of the prostate. No significant difference in the overall response rate was found between androgen and parathormone priming prior to radiophosphorus therapy. The degree of response was not dependent on total dose of 32P within the range of 9--18 mCi (333--666 MBq). Myelosuppression was a transient complication in 9 of 33 patients with metastatic breast carcinoma and in 7 of 15 patients with metastatic prostate carcinoma. Symptomatic hypercalcemia was an infrequent complication of radiophosphorus therapy irrespective of the priming regimen.