A three-dimensional finite element model was constructed to investigate the significance of poroelastic coupling between the 1992 Landers and Big Bear earthquakes in southern California. The homogeneous poroelastic model predicted a maximum increase in left lateral slip potential (change in shear stress less the change in effective fault normal stress scaled by a coefficient of friction) along the south-west part of the Big Bear fault, consistent with the epicentral location. In contrast, slip potential calculated for a weak fault zone in a state of isotropic stress for drained conditions, indicated a maximum increase along the northeast part of the Big Bear fault. ¿ 2000 American Geophysical Union