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