Aluminum has been recognized as being one of the important toxic metals encountered in clinical medicine and has been shown to have some potential biological function. It seems probable that all metals are toxic. Acute metal poisoning is encountered less commonly than chronic metal poisoning. Toxic metals, especially their ions, once absorbed into the body, will bind tightly to structural or cellular components, and this tendency complicates both the clinical picture and therapeutic approach to metal toxicity. A fairly complete picture emerges only for a few metals, namely, lead, mercury, and cadmium. These metals have been studied most intensively for one reason or another. Metallothionein analysis presents an advantage over cadmium metal analysis in that it is not subject to external contamination. Chromium absorption depends on the oxidation state of the metal. Mercury absorption depends on the form of the metal. Elemental mercury is well absorbed by inhalation.