Electromagnetic energy in the microwave and radiofrequency bands can produce biologic effects, which are predominantly thermal. During therapeutic use under medical supervision, desired biologic effects are produced and potentially injurious effects minimized. The biologic effects of electromagnetic fields have materialized because of a recent concern that relatively low-level fields produced by everyday electrical appliances, wiring in the home, and power transmission lines may be causally related to a number of detrimental health effects.