In a preliminary report on a small fraction of the projected subject population, some evidence in support of both sexual activity and venereal transmission hypotheses is accumulating. Prostatic cancer cases, in contrast to hospitalized and/or neighborhood controls, are beginning to show greater proportions of selected sexual activities compatible with venereal transmission of an infectious agent, such as number of sexual partners, use of prostitutes, prior venereal disease, and genital infections in the spouse. Patients with prostatic cancer also appear to have had higher fertility and more prostatic cancer in blood relatives than controls. Age at first intercourse and at first marriage are lower among the cancer patients than among the controls. Antibody titrations for herpesvirus and cytomegalic virus, although currently not revealing striking disparities in positivity, tend to show higher titers among the cancer cases.