The entropy generation for a fully developed turbulent fluid flow in a smooth duct subjected to constant wall temperature is investigated analytically. The temperature dependence of the viscosity is taken into consideration in the analysis. The ratio of the pumping power to the total heat flux decreases considerably when fluid is heated and the entropy generation per unit heat flux attains a minimum along the duct length for viscous fluids. The results corresponding to the temperature dependent and constant viscosity cases are compared. It is found that constant viscosity assumption may yield a considerable amount of deviation in entropy generation and pumping power results from those of the temperature dependent viscosity cases, especially when highly viscous fluids are considered. (C) 2000 Elsevier Science Ltd. All rights reserved.