Exposure levels of the principal carcinogenic and potential carcinogenic metal and metalloid pollutants in the environment (e.g., arsenic, beryllium, chromium, nickel, cadmium, and lead) are primarily reviewed with emphasis on their environmental sources both natural and manmade. There is a general paucity of definitive information concerning aspects of material balance and chemical transformations of these elements in various chemical forms in the environment, primarily the atmosphere. Estimates of both exposure levels and risk to populations other than industrial workers of the above metals have been in most instances quite difficult to obtain and generally speculative.