Benign and malignant prostatic tissue was removed in surgery and partitioned for (a) ultrastructural study, (b) tissue culture, and (c) (c) immunochemical study. Fourteen malignant and 18 benign prostatic cancer specimens were examined by transmission electron microscopy (TEM) for the presence of viruses or virus-like particles. Viruses could not be identified with assurity in thin sections. Acinar cells of normal, benign prostatic hypertrophy (BPH), and neoplastic prostate tissue were examined in the scanning electron microscope and TEM and found to be extremely heterogenous in their surface morphologies. Three major types of surface morphologies were present: microvillous, ruffled, and bare. All three types of cells were present in normal, BPH, and neoplastic acini. A collagenase procedure was utilized to remove the stromal cells from glandular structures prior to in vitro cultivation. Partially purified extracts from 71 human urothelial tumors and 75 human urothelial nontumor tissues were used as competing antigens in competition radioimmunoassay in an effort to detect the presence of one of the structural components of type-C ribonucleic acid viruses, the p30 core protein. The urothelial tumors tested included 42 BPH specimens and 18 prostatic carcinoma specimens. Thirty-eight percent of the prostatic carcinoma tissues and 48% of the BPH tissues demonstrated the presence of a protein antigenically similar to the p30 core protein of an oncogenic RNA virus.