A system for measuring intrathoracic impedance across a plurality of selected tissue segments, comprising: a lead carrying a plurality of electrodes, the electrodes being positioned on said lead so that, in use, selected pairs of the electrodes span selected ones of the plurality of selected tissue segments; means for injecting a low frequency current between the selected pairs of electrodes; impedance measurement circuitry configured to measure a magnitude of impedance and a phase angle of impedance between the selected pairs of electrodes to generate measured impedance magnitudes and phase angles for the selected pairs of electrodes of the low frequency; and processing circuitry configured to evaluate the measured impedances to determine whether the tissue segment is in a diseased condition, and to provide an indicator of disease based on the determination of whether the tissue segment is in a diseased condition, the processing circuitry comprising means for comparing at least one of the measured magnitude of impedance and the measured phase angle of impedance at the low frequency to a reference value of impedance magnitude and a reference value of impedance phase angle, respectively, established at the low frequency; means for evaluating at least one of a decrease in impedance magnitude from the reference value and an increase in impedance phase angle from the reference value, to determine whether the tissue segment is in a diseased condition; and means for providing an indicator of disease based on the determination of whether the tissue is in a diseased condition; and wherein an indicator of pulmonary edema is provided based on the increase in the measured phase angle of impedance from the reference value of impedance phase angle. a lead carrying a plurality of electrodes, the electrodes being positioned on said lead so that, in use, selected pairs of the electrodes span selected ones of the plurality of selected tissue segments; means for injecting a low frequency current between the selected pairs of electrodes; impedance measurement circuitry configured to measure a magnitude of impedance and a phase angle of impedance between the selected pairs of electrodes to generate measured impedance magnitudes and phase angles for the selected pairs of electrodes of the low frequency; and processing circuitry configured to evaluate the measured impedances to determine whether the tissue segment is in a diseased condition, and to provide an indicator of disease based on the determination of whether the tissue segment is in a diseased condition, the processing circuitry comprising means for comparing at least one of the measured magnitude of impedance and the measured phase angle of impedance at the low frequency to a reference value of impedance magnitude and a reference value of impedance phase angle, respectively, established at the low frequency; means for evaluating at least one of a decrease in impedance magnitude from the reference value and an increase in impedance phase angle from the reference value, to determine whether the tissue segment is in a diseased condition; and means for providing an indicator of disease based on the determination of whether the tissue is in a diseased condition; and wherein an indicator of pulmonary edema is provided based on the increase in the measured phase angle of impedance from the reference value of impedance phase angle.