The murine monoclonal CD3 antibody (OKT3) is effective in the treatment of refractory renal and cardiac allograft rejection and holds promise for improving rejection prophylaxis in heart transplantation. Although the administration of OKT3 is associated with many side effects, arteritis has not been previously reported. We report the development of acute necrotizing temporal arteritis associated with the deposition of mouse immunoglobulin G in a heart transplant recipient receiving OKT3 treatment of refractory rejection.