Abstract: Methods and apparatus are provided for determining the condition of selected regions of epithelial and stromal tissue. A plurality of electrodes are used to measure surface and transepithelial electropotential of tissue, especially breast tissue, as well as surface electropotential and impedance at one or more locations and at several defined frequencies, particularly low frequencies. An agent may be introduced into the region of tissue to enhance electrophysiological response characteristics. Measured and derived electrical properties facilitating diagnosis include DC potential, impedance, subepithelial resistance, epithelial resistance, capacitance, characteristic frequency, depression angle and transepithelial potential. Ambient and varying pressure measurements applied to epithelial tissue are also used for diagnosis. Improved diagnosis of tissue condition can be made based on the electrical properties and tissue electrophysiological response to altered ion transport and pressure.