Permeability and storage coefficients are essential parameters controlling fluid flow and pore pressure regime. Knowledge of these parameters under in situ conditions is therefore important in understanding deformation processes in accretionary complexes. Most permeability measurements on samples from the Nankai accretionary complex have been performed without pressure confinement (Taylor and Fischer, 1993) or at low confining pressure (<1 MPa) (Gamage and Screaton, this volume; Karig, 1993). Measurements of permeability under 1–5 MPa effective confining stress give lower values (Byrne et al., 1993). Here, we report measurements performed in the 0.5- to 2.5-MPa range in a triaxial cell with the main purpose of approaching in situ stress conditions. These measurements are indicative of the permeability of the unfractured sediment and may, therefore, constrain fluid flow out of the fault zones through the wallrock. The permeability of fractured zones may be higher, especially if the fractures are dilated because of a high fluid pressure. To investigate the effect of fracturing, samples were failed along drained paths at low (0.2 MPa) and relatively high (2.5 MPa) effective pressure and permeability was measured before and after fracturation. Slickenlined fractures formed during the failure tests with visual aspects similar to fractures observed on core samples, and it was possible to determine the friction coefficient of these surfaces. Experimental difficulties and time constraints limited the number of samples that could be processed; therefore, interpretations are preliminary.