An experimental study is reported of the effects of fluid property variation on turbulent heat transfer to water in a uniformly healed pipe. Data were obtained for bulk to wall viscosity ratios of up to 1.4 over a range of Reynolds numbers from 2.1 x 10(4) to 5.3 x 10(4). After establishing constant-properly values of heat transfer coefficient, the effect of variable properties was determined. This was expressed in terms of bulk to wall viscosity ratio raised to a power n. It was found that n increased steadily from about 0.1 to about 0.18 over the Reynolds number range covered, the mean value being close to the widely quoted Sieder and Tate index of 0.14.