The objective of this study was to improve the accuracy of net radiation (Rn) measurements under conditions conducive to dew or frost deposition. Two nonventilated net pyrradiometers were mounted over grass during November and December 1986. A heating element was located on the supporting arm of each radiometer so that heal would be conducted to the sensing head. Heat was applied to one radiometer for a few days, followed by a period during which no heat was applied. The procedure was repeated, alternating between radiometers throughout the experiment. Heating the radiometers successfully averted the deposition of dew and frost on the domes, which produced errors in Rn as high as 54 W m−2. The effect of heating alone was slightly asymmetric and resulted in a significant decrease in the mean Rn of 8 W m−2 relative to the unheated radiometer. This effect can be compensated for in the calibration of the radiometer.