A numerical model of dispersion of dyed sand tracers is developed. The model is based on a grid of cells which represent the domain of a tracer experiment. The dispersion of the tracer is simulated by specifying the trajectories (or, alternatively, the volumetric transport rates) of dyed and undyed grains between cells during a wave period. The model conserves tracer mass, and for symmetrical one-dimensional grain oscillations, the model is equivalent to a finite-difference approximation of the diffusion equation. By fitting the predictions of the model to the results of a field tracer experiment, the particle trajectories and sediment transport rates during the experiment may be determined. As an example, the model is used to simulate the tracer experiment of Inman and Chamberlain <1959>. The model reproduces the observed dispersion of tracer if 15% of the grains move 0.71 m during 1/4 wave period, and if the remaining 85% of the grains move 0.036 m during 1/4 wave period. The rapidly moving grains presumably travel in suspension, while the slowly moving grains probably travel as bed load. ¿American Geophysical Union 1987