Many over-the-counter products and therapies available to horse owners invo
lve the application of a magnetic field. Although the biologic effects of l
ow-level magnetic fields have been studied since the 1500s, there is no con
sensus regarding their physiologic significance. From a scientific standpoi
nt, the claims made for these products are not supported by incontrovertibl
e evidence. This article reviews the basis for magnetic and electromagnetic
therapy in horses and evaluates existing data from the literature.