Permeability and volumetric strain were measured under constant confining pressure and pore pressure as a function of increasing and decreasing differential stress. Permeability was found to increase appreciably during dilatancy. Our results have also shown that permeability and dilatant volume changes are not unique functions of differential stress and that permeability changes with differential stress are not uniquely dependent upon dilatant volume changes. Most significant, however, is that if dilatancy-fluid diffusion occurs in situ, our results indicate that microcrack dilatancy is not a reasonable physical mechanism to account for such a phenomenon.