Gravitational lensing of fluctuations in the microwave background radiation

We investigate the effects of gravitational lensing by clustered matter on fluctuations in the microwave background radiation. We derive a simple expression for the temperature autocorrelation function which shows that lensing produces a small enhancement to the variance expected in a beam switching experiment. For most models of galaxy formation the effects of gravitational lensing on the temperature fluctuations are negligible. Our conclusions disagree strongly with those of Kashlinsky who argues that gravitational lensing would erase fluctuations in the microwave background on arcminute scales.