Abstract: A method and apparatus for performing electrical measurement of body mutual electrical impedances to determine changes in total body water in normal and deranged states of the body. The apparatus is particularly useful in determining the progression of dialysis cases during the period when renal dialysis is being performed on the patient. The method and apparatus utilizes a special electrical circuit for measuring electrical characteristics at selected body locations. Certain electrical characteristics are measured such as the resistance, the capacitive impedance, and the total reactance of the body, and the phase angle is calculated or measured. Utilizing some of these measurements, the total body water relative to the body weight may be determined.