The precession of macroinstability (MI) vortices in stirred vessels has been investigated with vortex tracking methodologies, and utilized to enhance mixing performance. The techniques used are presented and employed to determine the instantaneous and average location, size and vorticity of the MI vortex for Re = 3,200 and 32,000 in 80 and 294 mm dia. vessels stirred by a Rushton impeller. Measurements of mixing time are performed in a 588 mm dia. vessel with surface insertion of a passive scalar tracer either inside or outside the precessing MI vortex. The data indicate that in-vortex insertion can result in a mixing time reduction of 20%, and even possibly 30%. (c) 2007 American Institute of Chemical Engineers.