Heterograft myringoplasty on dogs was performed. Serosa of the cecum of the calf was used in eight middle ears and cadaver tympanic membrane of the calf with the malleus attached in four. All canine eardrums were healed 10 to 12 weeks postoperatively. The heterografts were then unidentifiable. In only two middle ears did a mild inflammatory reaction occur with serosa grafts, but in three of the four middle ears with cadaver eardrum grafts, severe inflammation and scarring appeared. The attached denatured calf malleus was being remodeled into a canine ossicle by new bone deposits. The results with calf serosa graft indicate that tolerance and survival might be expected using it in the human ear. However, the experiences with the calf cadaver tympanic membrane suggest a need for great caution in expanding the present information to surgical use in the human.