Results of a study of heat transfer in the vicinity of a backward-facing step of a uniform temperature are presented. Temperature distribution are measured using a Mach-Zehnder interferometer. The heat transfer upstream of the step is shown to be strongly enhanced by streamline curvature. Downstream of the step the heat transfer increases monotonically in the streamwise direction but is always less than the flat-plate value. For the largest step investigated, the average heat transfer in the reverse flow region is reduced to 56 percent of the flat-plate results, in agreement with an existing theory for laminar separated flow originally developed for a cavity. The heat transfer is systematically smaller for smaller steps. For all steps, the average heat transfer is described by the equation, St = 0.787(Res)−0.55 (s/xs)0.72.