The peloid is seen to be a complex system of interrelationships in terms of the soluble cations, which can potentially be supplied to the patient's skin. These cations are mainly found in the Liqint bathing the mineral particles but closely related to the exchange cations on the mineral surface. As the solid phase of the peloid has an ionic exchange phase it becomes active, a reservoir of available ions which enhance the action of the peloid. This is not only restricted to cations but extends to polar pharmacologically active substances which can be sorbed in the peloid in ionic exchange positions of the mineral phase. These substances later pass from the exchange complex to the Liqint of the peloid and thence to the skin.