Abstract A statistical study was made of the mortality rates from arteriosclerotic and hypertensive heart diseases in the United States in relation to the concentration of manufacturing establishments. It was found that the mortality rates from these diseases as well as the concentration of manufacturing establishments vary greatly in the different states and regions of the country. With few exceptions, there is a definite parallelism between the death rates and the number of manufacturing establishments in the various states. Those states that have the highest concentration of manufacture generally have the highest mortality rates from these diseases. There is also a definite geographic distribution of both the manufacturing establishments and the mortality rates from these diseases, corresponding in location to the sequential expansion of settlements in the various parts of the country since colonial days. In general, those areas which were first settled and where industry was first established have the highest concentration of manufacture and mortality rates. The observations suggest that there is a multiplicity of factors associated with industrialization which contribute to the etiology of arteriosclerotic and hypertensive heart diseases. Some of the factors may be the smog-filled, poisonous air which we inhale in industrial areas: confined, indoor life; insufficient fresh open air recreation; pent-up emotions associated with monotony of automatic activity of the worker in this machine age; the rapid speed of work and travel in this restless age; and the extreme tensions under which we live. It is suggested that our future studies of the etiology of these diseases be broader in scope than heretofore, and should include the factors enumerated above. It is my belief that confining our attention only to the study of fat metabolism and dietary habits alone as causes is taking too narrow a view in the investigation of the underlying etiology.