The binding of 3H-R 1881 to cytosol prepared from benign and malignant prostatic neoplasms has been investigated. We have demonstrated that high affinity binding of 3H-R 1881 is present in cytosol preparations of benign prostatic hyperplasia, in specimens of prostatic cancer obtained from patients prior to hormonal therapy and in carcinoma of the prostate metastatic to lymph nodes. In addition, high affinity binding was present in all specimens of prostatic cancer from patients who had objective evidence of progressive metastatic disease after an initial response to hormonal therapy. Until greater numbers of patients have been studied the significance of these findings can only be speculative. Because the binding of 3H-R 1881 may measure androgen and progesterone receptors future investigations must include careful steroid specificity studies. Finally, because steroidal hormones exert their major influence within the nucleus of target tissues the measurement of nuclear receptor content may provide a more accurate means to predict the hormonal responsiveness of prostatic cancer.