We have found that anomalous electron temperatures in the disturbed high-latitude E region can be quantitatively explained in terms of heating by unstable plasma waves. The electron temperatures at 110 km have been measured to be as high as 1500¿K instead of the expected value of about 300¿K. We show by using quasi-linear theory that there is an ample source of heat in the unstable waves and that the measured electron temperature profiles have a shape very similar to what is expected from plasma wave heating by the modified two-stream instability. We find that there is even more heating going to the ion gas, but that the resulting effect on the ion temperature may be difficult to measure. Our best estimate of the wave heating rates leads us to conclude that wave heating can be as much as 50% of the Joule heating for dc electric field strengths of the order of 45 mV/m or greater.