A method for determining true formation pressure in formations surrounding a fluid-containing borehole having a mudcake on the surface thereof, including the following steps: at a particular location in the borehole, monitoring the electrokinetic potential across the mudcake; modifying the borehole pressure at the particular location in the borehole; and determining the true formation pressure in the formations surrounding the particular location as being the borehole pressure at which the electrokinetic potential is substantially zero.