For fluids which deviate from the law of Poiseuille, the kinetic energy term is usually ignored. In many cases this is justified since the experiments are performed under conditions where the correction is apparently negligible. The neglect of this factor in the flow of viscous liquids has caused many errors, and it is therefore desirable that some method of calculating the effect should be developed for other types of flow. The purpose of this paper is to calculate the kinetic energy correction by making use of general principles which apply to every possible case of flow, and also to obtain conclusions concerning the possible magnitudes of the correction.