Cardiovascular diseases are often found to be associated with certain physicochemical characteristics of the environment-namely, the hardness of the water and the types of rock and soil underlying the area. Areas supplied with soft water usually have higher cardiovascular death rates than do areas supplied with hard water. Evidence linking cardiovascular diseases with the geochemistry of rocks and soils is more limited. The nature of these associations is still speculative but it is possible that certain trace elements are involved, some being beneficial and others harmful. Further epidemiological studies to identify these various trace elements are desirable.