Planar laser-induced fluorescence of NO has been used to acquire instantaneous two-dimensional images of the extent of fluid unmixedness in a turbulent flow. Measurements accurate to the molecular diffusion scale are made by taking advantage of the large range of cross sections for electronic collisional quenching of NO A(2)Sigma(+). The recorded signal is known to be related to that fraction of the sample volume which contains pure (unmixed) fluid. Image measurements of an axisymmetric shear layer are presented and are reduced to mixed fluid probability distributions.