The idea of determining the onset of the Toms' phenomenon, based on the experimental flow resistance curves, is presented. Compared to the method proposed by Berman [3] a modification is introduced here, consisting in determining the onset from the crossing point of the measured resistance curves with the Prandtl-Karman-Nikuradse curve. The original experimental results are also presented, illustrating appearance of the drag reduction effect both in the laminar and turbulent flow regions.