It is obvious that, to the general public, environmental pollution determines the state of public health to a considerable extent. Scientifically, however, this relationship is less readily detectable, particularly when the environment polluted by chemicals is the polluted human environment. It is more correct to define 'environment' to include both the 'external' and the 'local' environment. The external environment includes a part which is directly affected by man, for instance when man-made chemicals are involved as well as the natural environment. The local or personal environment particularly concerns matters which may be comprised in the term 'lifestyle'. The above forms of environment may all affect health, although effects may differ in quality and quantity. These relationships are discussed, with special reference to the occurrence of cancer.