This work is a critique to a paper published in the International Journal of Heat and Mass Transfer 48 (2005) 4460-4466, which concerns the boundary layer flow of an electrically conducting incompressible fluid over a heated stretching sheet. The flow is permeated by a uniform transverse magnetic field and the fluid viscosity is assumed to vary as a linear function of temperature. In the published paper the calculation domain was small and the temperature profiles are truncated. Although the dynamic viscosity has been considered a function of temperature and consequently variable inside the boundary layer the Prandtl number, which depends on viscosity, has been considered constant inside the boundary layer. The results of the present work are obtained with the direct numerical solution of the boundary layer equations taking into account both viscosity and Prandtl number variation across the boundary layer. The temperature profiles of the present work are quite different from those of the above work. (C) 2007 Elsevier Ltd. All rights reserved.