Forty patients(25 patients of prostatic cancer and 15 patients of benign prostatic hyperplasia)were ex-amined with radioimmunodetection(RID) using antibody against r-seminoprotein(r-sm). The images of ma-lignant tumor sites were revealed from the scan of single photon emission computerized tomography with thetracing of dual radionuclide and computer digital subtraction technique. Of the 25 patients with prostatic can-cer texted, twenty-four were demonstrated in RID with a positive rate of 96%.The ratio of taking in nuclideradioactivity between the tumor tissue and normal tissue(T/N)was 6.9 and the best showing time was the96th hr from injection of radioactive antibody against r-sm.The minimum diameter of the tumor detected inRAID was 0. 5 cm. All of the 8 cases of metastatic prostatic cancer in pelvic or bone location were detected, Forty patients (25 patients of prostatic cancer and 15 patients of benign prostatic hyperplasia) were ex-amined with radioimmunodetection (RID) using antibody against r-seminoprotein (r-sm). The images of ma- lignant tumor sites were revealed from the scan of single photon emission computerized tomography with thetracing of dual radionuclide and computer digital subtraction technique. Of the 25 patients with prostatic can-cer texted, twenty-four were demonstrated in RID with a positive rate of 96%. The ratio of taking in nuclideradioactivity between the tumor tissue and normal tissue (T / N) was 6.9 and the best showing time was the 96th hr from injection of radioactive antibody against r-sm. the minimum diameter of the tumor detected in RAID was 0. 5 cm. All of the 8 cases of metastatic prostatic cancer in pelvic or bone location were detected,