The heat transfer characteristics of circular cylinders exposed to slot jet impingement of air has been studied experimentally. The study focused on Reynolds numbers (based on nozzle average exit velocity and cylinder diameter) in the range 600-8000. Both contoured orifice and sharp-edged orifice jet configurations were investigated for cylinder diameter-to-jet width spacings of 0.66, 1.0 and 2.0, and for jet exit-to-nozzle width spacings in the range 1 < z/w < 11. Reference measurements were made with the same cylinder in infinite parallel flow in a wind tunnel. The results reveal that the slot jet yields considerably higher average heat transfer from the cylinder when compared to the infinite parallel flow case on the basis of identical average velocity in the slot jet and infinite flow configurations. As with slot jet impingement heat transfer from flat surfaces, there appears to be a nozzle-to-cylinder spacing, scaled by nozzle width, which exhibits a maximum in heat transfer. The average heat transfer characteristics of the cylinder are correlated empirically. (C) 2000 Elsevier Science Ltd. All rights reserved.