Occupational hygiene is the measurement and control of the working environment with the object of safe guarding the health of people at work. Traditionally in Great Britain the two ways of approaching industrial health problems which have developed are those of the industrial medical officer from within the factory and the factory inspector through the medium of legislation. The approach of the industrial medical officer includes treatment of accidents and illness occurring at work, provision of first aid services, supervision of general factory hygiene, and advice to management on any question involving medical policy. He is not able, however, accurately to assess and control dust, fume, radiation, noise, and other hazards without the help of engineers and chemists trained in this work. Such help is at present almost impossible to obtain, unless the particular hazard is so spectacular or has such national importance or research interest as to engage the attention of the Medical Research Council or a special university department. The approach of the factory inspector is, in the main, that of a safety engineer, and it is to his credit that our industry is so well supervised from this standpoint. But the factory inspector is also charged with the preven tion of occupational disease, for example in Section 47 of the Factories Act 1937, which deals with the control of dust and fume " likely to be injurious or offensive ". For this task he is not well equipped, since he has no means of estimating whether a dangerous amount of air pollution is present and must depend on making an intelligent guess. He may seek the help of the engineering and chemical branch or call in one of the 16 medical inspectors. The latter are experienced in industrial hygiene but are expected to cover all factories in England, Scotland, and Wales. The medical inspectors have facilities for clinical examination and haematology but are limited in the number of radiographs which may be taken. Samples of the substance in use or of the air contaminant itself can be sent to the Government Laboratory but, because only occasional samples can be analyzed, few, if any, complete and repeated factory surveys can be made. A situation exists, therefore, in which many health hazards, particularly in small factories, remain un detected and, if known, cannot be controlled with certainty. We believe, in fact, that much occupational disease is never diagnosed or notified, and that discomfort due to working conditions, as distinct from actual