Five patients with respiratory disorders associated with hard metal exposure are described. In four patients electron microprobe analysis of bronchoalveolar lavage cells or lung tissue was used to show tungsten and other hard-metal components. Three patients had interstitial pneumonia and fibrosis with unusual multinucleate giant cells. Electron microscopy showed that the giant cells comprised both type II alveolar epithelial cells and alveolar macrophages. The multinucleate macrophages formed a distinctive feature of the bronchoalveolar lavage material but the multinucleate alveolar epithelial lining cells were evident only in lung tissue. The other two patients both suffered from work-related asthma, one of whom also had pulmonary opacities. Bronchial provocation tests in these patients supported the diagnosis of hard-metal-induced asthma and implicated cobalt as the agent responsible.Hard metal is an alloy of tungsten carbide, cobalt, and occasionally other metals such as titanium and tantalum. Because of its hardness and resistance to high temperature it is used to make drill tips, tool edges, and armament components. In the manufacturing process the raw materials are ball milled and the resultant dry powder is mixed with wax, pressed into moulds, and heated to 1000°C (presintering). The presintered hard metal has the consistency of chalk and can be easily cut into the required shape. The shaped article is then heated to about 1500°C (sintering) to produce hard metal, which can be worked only with a diamond. Ball milling, working the presintered metal, and grinding the sintered product are all processes liable to produce dust.Respiratory disease in the hard-metal industry has been recognised as a probable occupational hazard since 1940.' The initial reports emphasised interstitial lung disease but more recently asthma has also been described.

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