The performance of KM static mixers has been assessed for the blending of Newtonian and time-independent non-Newtonian fluids using planar laser induced fluorescence (PLIF). A stream of dye is injected at the mixer inlet and the distribution of dye at the mixer outlet is analyzed from images obtained across the pipe cross section. The effect of number of mixing elements, fluid rheology, and apparent viscosity ratio for two-fluid blending have been investigated at constant mixture superficial velocity of 0.3 m s(-1). Aqueous solutions of glycerol and Carbopol 940 are used as the working fluids, the latter possessing Herschel-Bulkley rheology. The PLIF images have been analyzed to determine log variance and maximum striation thickness to represent the intensity and scale of segregation, respectively. Conflicting trends are revealed in the experiments, leading to the development of an areal-based distribution of mixing intensity. For two-fluid blending, the addition of a high viscosity stream into the lower viscosity main flow causes very poor mixing performance, with unmixed spots of this component observable in the PLIF image. (c) 2013 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 60: 332-342, 2014