A new method has been proposed for estimating sensible heat flux from single-level measurement of air temperature. When turbulent transfer of heat in the lower atmosphere over a homogeneous surface is modeled by a one-dimensional diffusion equation with a constant diffusivity, heat flux can be expressed as a weighted average (half-order derivative) of the time history of air temperature. This formula provides an approximate solution of the diffusion equation where the (eddy) diffusivity characterizing the turbulent flow is not constant. Eddy diffusivity has been formulated based on Monin-Obukhov similarity theory with Businger-Dyer stability functions or determined by an empirical equation. The knowledge of surface parameters including friction velocity sometimes is needed to apply this method. The method was tested against observations collected during two field experiments, FIFE and ABRACOS. The close agreement between the estimated sensible heat flux and observations suggests that this novel approach is a potentially powerful tool in evaluating the energy balance at the land surface. ¿ 1998 American Geophysical Union