[General aspects of relay toxicity; its applications].

Chemical substances as feed additives, pesticides, drugs or natural toxicants, may enter in the body of farm animals. They are then accumulated, transformed in metabolites more toxic but, generally, less toxic than initial ingested compounds. Farm animals are a biologic active relay able to change entirely conclusions from a direct toxicological evaluation on laboratory animals. It must be also underlined that physical and chemical very sophisticated methods carried out for isolation of toxics are not always in agreement with "in vivo" assays. We must consider residues availability. The methodology called "relay toxicity" consists essentially on the submission of the animal product which contain a mosaic of residues available or not, to long term testing in laboratory animal as pseudo-consumers. So it is possible to measure influences of a lot of metabolite in a dietary context. For these reasons we are thinking it is an appropriate procedure, taking its place among the test to be undertaken for a biological and a more realistic evaluation of additives drugs, pesticides residues or natural toxicants in the feeds of farm reared animals whose meat, eggs or milk will be eaten by human consumers.