Forty-six patients with histologically proved adenocarcinoma of the prostate underwent pelvic lymphadenectomy after CAT scanning. The accuracy, specificity, and sensitivity of the CAT scan in detecting nodal metastasis were 70, 93 and 30 per cent, respectively; this compares favorably with pedal lymphangiography. Seventeen of the patients had radical prostatectomy. The accuracy, specificity, and sensitivity of the CAT scan in depicting local extent of the tumor were 47, 100, and 18 per cent, respectively; although low, no other clinical or biochemical method provides a better result.