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The mortality of men employed in a plant manufacturing nickel alloys from metallic nickel and other metals has been examined. The plant has operated since May 1953, and 1925 men were identified who had been employed in the operating areas at the plant, other than as members of the staff, for a total of five or more years, excluding breaks. Analysis of samples of air obtained from personal samplers showed that since 1975 most of the men are likely to have been exposed to average concentrations of nickel of between 0-5 and 0 9 mg Ni/m3. All but 22 (1*1 %) of the men were successfully traced to 1 April 1978 or until they died or emigrated. One hundred and seventeen had died. The numbers of deaths observed from cancers of respiratory and other sites, other respiratory disease, ischaemic heart disease, and other causes of death were compared with the numbers expected from national and local mortality rates. No evidence of the existence of any occupational hazard was obtained. The number of deaths from lung cancer (15) in men employed for five years or more is small. At 98 % of the number expected at local rates it is statistically compatible with risks of between 0 5 and 2-2 times "normal."Work in nickel refineries in Canada, Norway, the USSR, and Wales has long been known to be associated with an increased risk of developing bronchial or nasal sinus cancer (see Sunderman' for review). The risk was at one time substantial; but despite this, it has not yet been possible to define precisely the conditions under which it occurred. Metallic nickel is carcinogenic in laboratory experiments in which it is injected into the muscles, pleura, or marrow of rats,2 but it does not necessarily follow that pure nickel is the responsible agent in man. The occupational cancers that have been observed were associated particularly with high temperature oxidation of nickel ore in some obsolete processes ofcalcining and sintering, and it is possible that the risk was characteristic of exposure to nickel subsulphide, which is the compound of nickel that most readily produces bronchial carcinoma in inhalation experiments on rats.3 Alternatively, it may have been due to a mixture of sulphides, oxides, and metallic nickel which are individually less active in laboratory experiments.2 We have, therefore, examined the mortality experience of men employed at Henry

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