The Analytical Chemistry Group of the Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has established new methods and standardized old ones for the biological monitoring of numerous industrial chemicals. The analytical reliability and reproducibility of each of the methods has been determined by the author and confirmed by at least one examiner. The methods are therefore suitable for checking adherence to statutory limits such as the German BAT values (Biological Tolerance Values for Working Materials) and the American BEI values (Biological Exposure Indices) and for reliable detection of dangerous substances in the tissues of individual workers.