A bay Standardbred mare, 6 years old, was admitted to Stange Memorial Clinic Sept. 22, 1947, with the history that she appeared to be in continuous estrum. Upon examination, it was noted that she strained following each act of urination. A dirty, creamy discharge exuded from the external genitalia and caused "scalding" of the perineum and medial sides of the thighs. Examination of the vagina revealed a thick diphtheritic membrane adherent to the vaginal mucosa. The discharge was due to the chronic necrotic condition of the vaginal mucous membrane.