The IRSST's researchers must answer questions on the application and usefulness of biological monitoring in different exposure scenarios. However, the uncertainty associated with the results of biological monitoring must be taken into consideration if decisions concerning exposure limits are to be well-founded. This research activity is aimed at creating a computerized tool to calculate, for a given number of samples, a threshold of confidence based on total variability. It will therefore be possible to calculate concentration ranges that are higher or lower than the reference values for each substance presented in the Guide de surveillance biologique - Prélèvements et interprétation des résultats (Biological Monitoring Guide - Samplings and Interpretation of Results) published by the IRSST. Slated for dissemination on the Institute's web site, this computerized tool will allow occupational health stakeholders to carry out more effective biological monitoring.