Summary This guide is meant for Québecers who work in occupational health. The goal is to provide crucial information about collecting samples for analysis. The guide has two sections. In the first section, a number of theoretical concepts regarding use of biological monitoring are examined. In the second section, toxicological tests available at the IRRST are listed and the related procedures for collecting and mailing samples and communicating analytical results are described. Contaminant data sheets summarizing current scientific knowledge for interpreting biological monitoring data are provided for 33 chemicals in a second document entitled Biological Monitoring Guide - Sample Collection and Interpretation of Results (in French only). Utilities for interpretation of the results are also available. We hope this guide will help those who work in occupational health in planning their activities and will provide guidance in selecting the best tests to use to assess worker exposure.