It has long been recognized that there is a relationship between environment and health and examples of this association are easy to cite—overcrowding tends to spread infection. But our knowledge of the exact part played by occupational as distinct from economic and social environment is as yet imperfect.' The liability of the worker to ill-health, apart from any inborn constitutional weakness, is determined broadly by two factors. The first is the influence of the type of work directly upon the worker, an influence inherent in the actual occupation and the conditions under which the work is done. This might be regarded as the direct occupational risk. The second is the economic and social environment conditioned by the occupation followed: this might be termed the indirect occupational risk. This distinction was recognized by the Eegistrar-General who stated that both factors are essentially components of the total occupational risk since ' If a man is obliged by his place of work and his rate of pay to live in an insanitary area, the extra risk of death involved is, in a wider but very real sense, part of the occupational risk'. The purpose of the present paper is to try to disentangle the parts played by each in determining the occupational mortality from a specific disease like tuberculosis. The difficulty which previously presented itself was the absence of a standard which could be regarded as a measurement of the indirect occupational risks. The Registrar-General, in his last Occupational Mortality Supple-ment, has provided an approximate index, by publishing data on the mortality of males following particular occupations and also that of their wives. His viewpoint was.'. for no trade could longer be regarded as directly prejudicial to health if it were found to entail as much excess risk for the wife as for the husband. In such a case excess mortality would evidently be in the main attributable to the social conditions implied.' Greenwood likewise stated that ‘the wives share the social and geographical advantages of their husbands’ occupation but, with relatively ummportant exceptions, are not exposed to their specific occupational risks’. The purpose of the present paper is to try to disentangle the parts played by each in determining the occupational mortality from a specific disease like tuberculosis. The difficulty which previously presented itself was the absence of a standard which could be regarded as a measurement of the indirect occupational risks. The Registrar-General, in his last Occupational Mortality Supplement, has provided an approximate index, by publishing data on the mortality of males following particular occupations and also that of their wives. His viewpoint was. ‘..for no trade could longer be regarded as directly prejudicial to health if it were found to entail as much excess risk for the wife as for the husband. In such a case excess mortality would evidently be in the main attributable to the social conditions implied.’ Greenwood likewise stated that ‘the wives share the social and geographical advantages of their husbands’ occupation but, with relatively ummportant exceptions, are not exposed to their specific occupational risks'.