This study was conducted to determine the efficacy of the male mouse as a model for epididymitis caused by human genital serovar E, Chlamydia trachomatis. C. trachomatis was reisolated from all tissues removed on Days 3, 5, and 7 post inoculation (pi). Although some infected epididymides removed on Days 10, 14, and 21 pi were positive, control tissues remained negative. Histopathology of tissues showed a heavy, mixed inflammatory infiltrate consisting of polymorphonuclear cells and lymphocytes. Serum antibody to C. trachomatis was detected in the infected mice only (titer greater than or equal to 1:32). Chlamydial inclusions and individual elementary bodies were confirmed by immunofluorescent and immunoperoxidase staining up to Day 7 pi. These data show that the male mouse is susceptible to C. trachomatis infection and is appropriate for studies dealing with the effect of C. trachomatis on male fertility.