Technical Abstract: The development of a new approach based on bioelectrical impedance data, called the R-Xc graph, offers the possibility of following the fluid status of an individual without reliance on previously developed prediction models. The R-Xc graph relies on a comparison of measurements of resistance and reactance that are divided by the individual's standing height and plotted on a two dimensional system. The vector that results is compared to reference data from healthy people of the same gender. The reference data are symbolized as an ellipse. If a vector is within the ellipse, the individual is considered to have normal hydration. The advantage of this new approach is that it permits a longitudinal assessment of fluid status independently of body size. If this approach is to gain general acceptance among clinicians, the sensitivity and accuracy of the vector must be established with standard dilution methods and comparisons with independent clinical measurements related to prognosis. If these important validation issues can be resolved, then the R-Xc graph may become a useful tool in management of patient care in a variety of medical environments.