Cobalt is a relatively rare magnetic element with properties similar to iron and nickel. The two valance states are cobaltous (II) and cobaltic (III) and the former is the most common valance used in the chemical industry. Cobalt occurs in nature primarily as arsenides, oxides, and sulfides. Most of the production of cobalt involves the metallic form used in the formation of cobalt superalloys. The term "hard metal" refers to compounds containing tungsten carbide (80-95%) combined with matrices formed from cobalt (5-20%) and nickel (0-5%). For the general population, the diet is the main source of exposure to cobalt. In the occupational setting, exposure to cobalt alone occurs primarily during the production of cobalt powders. In other industrial exposures (e.g., hard metal, diamond polishing), additional agents (tungsten) modulate the toxicity of cobalt. Cobalt is an essential element necessary for the formation of vitamin B12 (hydroxocobalamin); however, excessive administration of this trace element produces goiter and reduced thyroid activity. In 1966, the syndrome "beer drinker's cardiomyopathy" appeared in Quebec City, Canada, and was characterized by pericardial effusion, elevated hemoglobin concentrations, and congestive heart failure. An interstitial pulmonary fibrosis has been associated with industrial exposure to hard metal dust (tungsten and cobalt), but not to cobalt alone. Exposure to cobalt alone produces an allergic contact dermatitis and occupational asthma. Treatment of cobalt toxicity is primarily supportive.