We have used an immunoaffinity system whereby immunoglobulin from patients with prostatic carcinoma was coupled to solid phase protein A; the immobilized IgG was subsequently exposed to radiolabeled antigen from autochthonous or allogeneic primary tumor extracts or to radiolabeled antigen from a nude mouse-supported prostatic carcinoma cell line. Material specifically bound by prostatic carcinoma patient immune IgG was quantitatively eluted from the immunoadsorbent and characterized with regard to molecular weight. Sequential adsorption analyses of patient sera with normal human tissue pools, normal prostatic tissue, prostatic carcinoma tissue, and tissue from other urogenital malignancies has allowed a definition of those antigenic specificities relevant in the immunobiology of prostatic carcinoma. The patient humoral response was observed to be directed primarily toward a complex array of antigens representing normal human tissue components; serorecognition of prostate tumor associated antigens was discernible from that of common tissue antigens only after rigorous adsorption analyses. Preliminary results indicate that the prostatic cancer patient humoral antibody response may be directed toward either altered histocompatibility complex antigens or toward antigens physically associated with histocompatibility complex antigens.