Trace element deficiencies, toxicities and imbalances in man are more difficult to relate to geochemical factors than they are in farm animals. The reasons for this are discussed and examples of such differences between man and grazing animals presented. The most convincing evidence of a geochemical causal link with human disease comes from the incidence and distribution of endemic goitre. The influence of technological developments upon this relation is discussed. Other associations between the physical environment, including the air and drinking water, and to health are given and critically examined in relation to the criteria necessary to distinguish between association and causation. The nature and extent of man-made modifications of the natural geochemical environment through technological change are discussed in relation to intakes of Fe, I, Zn, Pb and Se and their relation, in turn, to human health and disease. The currently proposed permissible limits or maximum tolerances of potentially toxic elements are presented, and the importance to these tolerances of the chemical and physical forms of the element and their metabolic interactions with other elements is emphasized.