This study reports on 72 young soldiers who suffered from a recent epidemic of acute mumps, with special emphasis on 19 who suffered from mumps orchitis and whose spermograms were in the fertility range. The immunological work-up for antibodies in sera or seminal plasma gave normal results for the patients diagnosed with orchitis, as well as the controls. The only remarkable finding was an increased risk of borderline significance for orchitis in smokers. The present study has proven that the presence of antisperm antibodies does not play a role in the etiology of mumps orchitis.