A hot-wire pyrometer for measuring gas temperatures with a high sensitivity has been developed. The method can easily be extended to measurements of surface temperature. The principal elements of a hot-wire pyrometer are a fine wire inserted into the gas and a photomultiplier for measuring the radiation emitted from it. The output voltage V of the photomultiplier is shown both theoretically and experimentally to be the following function of wire temperature T: V=σT7/4 exp(−γT−1/2), where σ and γ are the calibration constants unique to a particular system.