ABSTRACT: Initial investigation demonstrated antibodies to sperm (ASA) in patients with benign prostatic hypertrophy (BPH) and prostate cancer (PCa). The occurrence of ASA under a variety of normal and pathological circumstances indicated the need for confirmation and extension, including delineation of their possible disease-associated specificity and implications. As countercurrent Immunoelectrophoresis (CIEP) employing sonicated allogeneic sperm (Sp) extracts appeared most efficient from initial studies of ASA, CIEP was employed for the present further study of 200 serum specimens from patients with and without prostatic disease. While ubiquitous, the continuing presence of ASA in BPH and PCa, with a combined incidence in this study of 57(52%) of 109 vs. 9 (10%) of 91 in the absence of prostatic disease remains provocative in view of the hypothesized role of Sp in the development of BPH and PCa. The presence, however, of ASA in patients with genitourinary neoplasms other, than prostate, raises doubt as to their disease specificity. Implications of ASA, other than in their more commonly related role in infertility, including their cross-reactivity with foetal antigens and lymphocytes and higher incidence in association with tumours and the presence of tumour-associated immunity are considered. However, pending further investigation, the present data may most appropriately be viewed as being reflective of a host response (marker?) to aberrant genitourinary cellular alterations.