A microtitre plate format enzyme linked immunosorbent assay (ELISA), employing commercially available PASE/4LJ mouse monoclonal hybridoma antibody is described. The technique is a solid phase indirect ELISA for prostatic acid phosphatase, applicable to specific detection of semen. Maximal detectability was found to be one hundred thousand fold dilution of pooled seminal plasma. No cross reactivities with human vaginal fluid, blood, saliva, female urine, nasal discharge, earwax, sweat or faeces have been found.