The processes of entrainment and mixing are investigated in a nonreacting, uniform density, liquid mixing layer. Laser-induced fluorescence diagnostics and high-speed, real-time digital image acquisition techniques are combined to measure the probability density function of the composition field. Results show that the vortical structures in the mixing layer initially roll up with a large excess of high-speed fluid in the cores. It is found that the mixed fluid composition, above the mixing transition, is essentially uniform across the entire transverse ex-tent of the layer and is asymmetric with a bias in favor of the high-speed fluid. Preliminary observations indicate that the composition of the mixed fluid is more uniform across a liquid shear layer than that in the gaseous layer. The important effect of the resolution capability of the measurement apparatus on me results are discussed and comparisons with recent theoretical calculations are presented.