A method of detecting a change (that is, an increase or a decrease) in thelevel of fluid in tissue in a first area of a body includes the steps of:applying electromagnetic energy, preferably in the frequency range ofapproximately 300 MHz to approximately 30 GHz, to a first volume of the body；measuring a resultant or returned signal； comparing the signal to a referencesignal to determine if the fluid level in the tissue has changed. In oneembodiment, the method detects changes in the level of fluid in tissue of abody by applying electromagnetic energy to a first volume of the body over aperiod of time (for example, using an antenna or antennae)； measuring aresultant signal or a signal returned from the tissue； and comparing thesignal to a reference signal to determine if a level of fluid in the tissuehas changed during the period of time.
