A method of determining parameter values used in impedance analysis of a subject.The method includes using a processing system to determine a number of impedancemeasurements at a corresponding number of frequencies. The impedance measurementsare used to determine estimates of parameter values, with the estimates beingused to determine theoretical impedance values based on the parameter valueestimates. The theoretical impedance values are compared to the measured impedancevalues to allow a modification direction to be determined for at least one of theparameter value estimates. This is then used to modify at least one parametervalue estimate, with the parameter values being determined at least in part fromone or more modified parameter value estimates.