The increasing number of women in the workplace has made it more important than ever to ensure a safe work environment, particularly with respect to mothers who choose to breast-feed their babies. The Quebec Commission de la sant? et de la s?curit? du travail (CSST) Toxicological Index is fully involved in the provincial program for the protective reassignment of workers who breast-feed infants. The Infotox database provides peer-reviewed information concerning chemicals identified in the workplace that may appear in the mother's milk, possibly to be ingested by the breast-fed infant. Data extracted from the CSST computer system that holds information on 5,500 substances are presented. A total of 153 chemicals (2.7%) are recognized as being involved in some milk transfer. The strength of evidence is assessed with reference to strong or weak association (excretion or detection) in humans or in animals. Such an effect provides a useful basis for administrative decision involving protective reassignment as well as evaluation of work environment. Database users must be well informed about the identification of chemicals in breast milk because this is an essential step for the evaluation of the hazards of transferring chemicals encountered in the workplace from mother to baby. Actually, the main problem is that there are very few data in the scientific literature concerning milk transfer.