The persistence of large anomalous electron heat transport in regions of improved ion confinement sometimes observed in tokamak plasmas suggests that the electron-temperature-gradient-driven drift waves may be the antecedents of the small-scale turbulence and associated energy flow. Whereas most previous investigations of these modes were carried out for a two-species plasma, in this study we retain impurities and examine their effects using gyrokinetic simulations supported by interpretations based on a simple analytic model. The inclusion of impurities is found to have a strong stabilizing effect on the electron temperature gradient modes.