[en] Some general aspects of occupational hygiene and health physics are discussed in relation to exposure to chemical and physical agents. Consideration is then given to the development of malignant disease in the lungs due to asbestos and in the bladder due to chemical carcinogens; these effects are compared to carcinogenic effects of ionising radiation. The mechanisms of lung cancer production by asbestos and bladder cancer by chemicals appears to be similar to that of ionising radiation, i.e. the probability of the development of the disease is associated with the level of exposure. However workers are continually exposed to low level radiation from natural background, potassium 40, medical procedures and world wide fall-out. Thus this presents problems in distinguishing between radiation induced cancer and cancer due to other causes. It is suggested that an accurate epidemiological assessment of persons exposed at or below the recommended dose limits for radiation is required. (UK)