Naturally a prospector prefers to find an outcrop of ore rather than discover an area which merely offers encouragement for further investigations. However as outcrops of ore become harder and harder to find and as the search for new mines intensifies, the discovery even of an area which justifies further detailed study becomes increasingly important.Just as mineralogists and geologists have turned to indirect methods, such as pathfinder minerals and ore halos, for help in their search for ore, so the biogeochemist may well turn to a study of elements, which although they may not be those that are being sought, may, by their presence in abnormal amounts, suggest anomalous conditions which in turn may justify a detailed search for ore in a particular area.This introductory paper describes our preliminary investigations into the practicability of using iron and manganese as biogeochemical pathfinders. These investigations are not an attempt to solve the complex problem of the iron and manganese distribution in trees; the aim is merely to show how iron and manganese vary not only in different organs but also in the same organs of trees if the trees have grown under different conditions. Naturally we have been particularly interested in the biogeochemistry of areas where there are known to be unusually high or low amounts of iron or manganese in the subsoil. Brief mention will be made of possible correlations between our work and some current hypotheses concerned with the relationships which may exist between the iron and manganese contents of plants.