Holographic interferometry is used to study heat transfer in Newtonian liquids flowing around a circular cylinder. Temperature differences are of the order of 0.1°C. Consequently, physical property variations are negligible. Isotherms, and local and mean Nusselt number data are obtained for water, corn syrup and dilute corn syrup, covering a Reynolds number range of 0.002–64 and Gr/Re2 of 0.001–4.4. The Prandtl number range is from about 5.5 to 27000. The isotherms and local Nusselt numbers clearly show evidence for the twin vortices at Reynolds numbers greater than about 5. The mean Nusselt number in this entire Reynolds number range can be correlated by a single equation. This is in contrast with previous investigators who employed two equations for Reynolds numbers greater than and less than one. The magnitude of natural convection effects for water is in agreement with previous investigators. However, the value of Gr/Re2 at which natural convection starts to become important is found to increase with Prandtl number.