In 62 patients with histologically confirmed carcinoma of the prostate bone scintigraphy, radiographic survey and serum prostatic acid phosphatase determinations were carried out to evaluate the progression of the disease and to compare the relative sensitivity of the diagnostic tools. Thirty-five patients had scintigraphic evidence of skeletal metastases, whereas abnormal X-ray survey and elevated prostatic acid phosphatase levels were found in only 4 and 19 patients, respectively, all of whom had positive scintigraphic findings. Radiographic evidence of metastases was not found in any of the patients with normal scintigraphy, while elevated prostatic acid phosphatase was found in two patients. It is concluded that bone scintigraphy is far more sensitive than either radiographic survey or determination of prostatic acid phosphatases in the diagnosis of skeletal involvement in prostatic carcinoma, and should be the method of choice for this purpose.