Using a one-dimensional gasdynamic model, it has previously been shown that pickup ions (PIs) play a significant role in the propagation of shock waves in the outer heliosphere. The effect of adding a magnetic field to the heliospheric model and the resultant effect on shock wave propagation are studied here. In the absence of PIs the addition of a magnetic field has a significant effect on shock wave propagation, yielding results very different from those obtained by simple gasdynamic models. When PIs are included, the difference between the gasdynamic case and the MHD case is quite small, indicating the dominant role played by the PIs. The difference between shock propagation characteristics when PIs are included and when they are ignored is not nearly as great in the MHD case as it is in the gasdynamic case. One of the main differences in the MHD case is the propagation of pressure-balanced structures (PBSs), which are shown to be more easily observed in the outer heliosphere when PIs are included. Besides PBSs, the inclusion of a magnetic field also allows for the investigation of structures such as magnetic clouds which can obviously not be studied using a gasdynamic model. ¿ 1999 American Geophysical Union