The quantitative characteristics of vortex structures and turbulent events in turbulent channel flows with and without drag reduction were investigated experimentally. Drag reducing aqueous solutions of CTAC (CTAC-cetyltrimethyl ammonium chloride) with concentration of 25 ppm and 75 ppm at 30 degrees C were tested. Particle image velocimetry (PIV) was used to measure the instantaneous velocity field in the streamwise-wall-normal plane of the flow. Through visualizing the instantaneous vector fields, contour maps of the swirling strength and instantaneous value of uv (u and v are the streamwise and wall-normal velocity fluctuations, respectively), the characteristic angle of vortex packets was quantified. It was shown that the drag-reducing CTAC additive reduced both the strength and frequency of turbulent bursts near the wall, and the characteristics of vortex structures and bursts were not only dependent on drag-reduction level but also on concentration of additive. From the quantified parameters characterizing turbulent events in a wall-bounded turbulent flow, it was obtained that f(T) was linearly proportional to the product of frequency and strength of turbulent events. (C) 2007 Elsevier Ltd. All rights reserved.