When faced with local chemical pollution, the decision arises as to whether to conduct a study using one or more biomarkers, as well as how to carry it out. This guide, developed by the French Institute for Public Health Surveillance, provides valuable methodological guidance for assessing the relevance of a local biomarker study and, if appropriate, proceeding with its implementation. Intended for public health professionals, it is divided into two parts: the first presents the five steps for determining the relevance and feasibility of a biomarker study in the context of local pollution. The second part provides practical advice for conducting a local biomarker study through 13 practical fact sheets. The factors to consider when deciding whether to implement a local biomarker study are thus outlined in the first part in the form of questions and answers: - What are the key elements of the environmental and health situation? - What would a biomarker study contribute to the management of the local situation? - What scientific objectives should a biomarker study address to be useful in defining management actions? - Are there one or more relevant biomarkers in the local context? - Is a biomarker study at the local level feasible? In the second part, the practical guides cover all the issues the investigator will face when implementing a local biomarker study, from engaging with the population to interpreting and communicating results, including participant inclusion and exclusion criteria, ethical and regulatory considerations, questionnaire design, the organization of sample collection and analysis, statistical considerations, etc. (R.A.)