The role of two-way interphase coupling effects in subharmonically forced, dilute, particle laden mixing layers is investigated. Temporally growing Lagrangian-Eulerian numerical simulations address both uniformly as well as differentially seeded flows. Emphasis is placed on a vorticity-based interpretation of the simulation results. Expanding the fluid vorticity source term due to two-way coupling demonstrates the importance of particle concentration gradients and 'slip vorticity'. For uniformly laden mixing layers and intermediate St particles, the reduction in the growth rate of the Kelvin-Helmholtz instability by the two-way coupling effects also slows down vortex pairing. At large St, a layered vorticity structure in the outer regions of the vortex cores results from the thick or even double banded nature of the braids. By causing the vortices to rotate around each other, the subharmonic forcing also enhances the particle transport away from the center of the mixing layer. Intermediate St particles are seen to benefit the most from this mechanism, so that they can, at least temporarily, exceed the dispersion rate of the passive case. For differentially loaded mixing layers, the vorticity source term is seen to cause an asymmetry in the pairing process, by weakening the upstream and strengthening the downstream vortex, which subsequently dominates the pairing. For intermediate St particles, this asymmetry leads to a more rapid ejection of particles from the downstream vortex. For large St particles, the braid region in between vortex pairs is seen to thicken and to roll up, thereby causing the emergence of a satellite vortex. Somewhat surprisingly, the results indicate that in a streamwise averaged sense the two-way coupling effects do not significantly alter the integral particle dispersion measure for subharmonically forced, differentially loaded mixing layers. Throughout, frequent comparisons with experimental data are made. (C) 2002 Elsevier Science Ltd. All rights reserved.