A new deuterium nuclear magnetic resonance (2H NMR) method is described for determining total body water in humans. The method has been validated against a standard infrared absorption (IR) procedure using a tracer dose of deuterium oxide (2H2O) of approximately 10 g for each human subject. The precision and accuracy for the methods have been compared and found to be very similar. The advantages of the 2H NMR method over other presently available techniques that are based on 2H2O dilution are as follows: it is fast, accurate, needs only a small dose of 2H2O, can be done using any body fluid, and, most importantly, does not require any sample preparation.