Summary This guide is meant for Québecers who work in occupational health. Our goal is to provide crucial information about the theoretical bases of biological monitoring and about interpreting analytical results. A number of theoretic concepts regarding the use of biological monitoring are described, and a strategic approach for using data obtained is presented. This approach takes into consideration the different objectives of workplace interventions, as well as biological variability and a number of other determinants related to the substance, the biological parameters and the nature of the exposure. This new edition of the biological monitoring guide updates the scientific knowledge and reference values for all chemicals in the preceding edition of the guide. New contaminant data sheets have also been added for dichloromethane, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate and toluene diisocyanate. In addition, a section has been added on adjusting urine analysis results for concentration dilution of the urinary sample. Lastly, a strategy for interpreting biological monitoring results is proposed for cases when the number of samples is small. The research team hopes the knowledge and tools provided will help those who work in occupational health to plan their activities and will provide guidance for selecting the best strategy to assess worker exposure.