A working party of the Commission of Toxicology of the International Union of Pure and Applied Chemistry has been set up to establish criteria to ensure analytical quality in the biological monitoring of toxic metals. Although the project has not yet been completed, some useful guidelines have been produced. They pertain to the description of the subject (so as to allow classification into a given "reference group"), the collection, storage and sampling of body fluids for trace-element determinations, and criteria to ensure the application of the correct analytical procedure, together with a quality-assurance protocol. It was agreed that a dedicated sampling protocol is required for each trace element in a particular matrix. Although it is impossible to specify this protocol together with all subsequent procedures in precise detail, the members of the working party have laid down general rules to be followed. This paper summarizes what has been achieved to date.