In Great Britain there have been no published reports of respiratory disease occurring amongst workers in the hard metal (tungsten carbide) industry. In this paper the clinical and radiological findings in six cases and the pathological findings in one are described. In two cases physiological studies indicated mild alveolar diffusion defects. Histological examination in a fatal case revealed diffuse pulmonary interstitial fibrosis with marked peribronchial and perivascular fibrosis and bronchial epithelial hyperplasia and metaplasia. Radiological surveys revealed the sporadic occurrence and low incidence of the disease. The alterations in respiratory mechanics which occurred in two workers following a day's exposure to dust are described. Airborne dust concentrations are given.The industrial process is outlined and the literature is reviewed. The toxicity of the metals is discussed, and our findings are compared with those reported from Europe and the United States.We are of the opinion that the changes which we would describe as hard metal disease are caused by the inhalation of dust at work and that the component responsible may be cobalt.Hard metal is manufactured by a process of powder metallurgy from tungsten and carbon with cobalt as a binder. The industry, starting in Germany after the first world war, has greatly increased in size. The extremely hard product (90 to 95 % the hardness of diamond) is used for the cutting edges of tools, rock drills, broaches, and dies. It is also used for radiotherapy screens and armaments.The process of manufacture involves the production of tungsten metal powder and cobalt powder from their respective oxides or salts. The tungsten metal powder is mixed with carbon and heated in an atmosphere of hydrogen to form tungsten carbide. Titanium carbide is added in some grades and is similarly formed. Small amounts of tantalum carbide and vanadium carbide may be incorporated in particular grades.The percentage by weight of tungsten carbide varies from 80 to 90, of titanium carbide 8 to 18 and of cobalt 5 to 25. More than three-quarters of production is of grades containing between 6 % and 9 % of cobalt.Carbides and cobalt are mixed wet in a ball-mill and dried. The dried powder is pressed to the required shape combined with wax using a solvent such as trichlorethylene, which is then driven off by heat in an oven in an atmosphere of hydrogen (presintering). After shaping, the product is heated again in an atmosphere of hydrogen (sintering). It is then ground, wet or dry, with diamond and carborundum wheels to its final shape.

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