Wallace, J., Sweetnam, P. M., Warner, C. G., Graham, P. A., and Cochrane, A. L. (1971).Brit. J. industr. Med.,28, 265-271. An epidemiological study of lens opacities among steel workers. To investigate the relationship between the prevalence of cataract and heat exposure, two groups of steel workers, differing widely in their heat exposure, were examined. Estimates of heat exposure were based on detailed industrial histories and (a) subjective estimates of heat exposure associated with various occupations and (b) actual measurements. Only two cases of cataract were found that would be generally accepted as `occupational' in origin, but a higher prevalence of the common form of cataract was found in the heat-exposed group than in the non-exposed group.