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. (C) 1997 Published by Elsevier Science Ltd.