The horizontal transport of particles by solitary internal waves is investigated using a fully nonlinear numerical model. The effect of an additional constant velocity Ud due to another physical mechanism such as surface wind drift or swimming motion in the case of live organisms is also considered. Weakly nonlinear theory is used to derive approximate analytic expressions for the transport distance of surface particles. The theoretical results are compared with transport distances obtained using the numerical model. The numerical model is also used to determine the vertical dependence of the horizontal transport. Two stratifications are considered. For one, with the strength of the stratification increasing monotonically toward the surface, the agreement between the theoretical predictions and the model results is excellent right up to the breaking amplitude. For the second, with a pycnocline between weakly stratified upper and lower layers, the nonlinear waves in the fully nonlinear numerical simulations are much wider than those predicted by weakly nonlinear theory. As a consequence, weakly nonlinear theory significantly underestimates the transport distance. It is found that significant particle transport occurs only when the waves are near the breaking amplitude, when they are very long, or when Ud plus the wave's surface current is comparable to the wave's propagation speed.¿ 1997 American Geophysical Union