This paper goes through the chemical risks able to affect the organic and the conventional agro-food products. For each type of contaminant a tentative assessment has been made in considering not only the levels of exposure but also the toxicological data when available. When comparing both production systems with regards to food safety, it appears that, for the well-known toxicants (pesticides, nitrates), organic products present some clear advantages, but it is also recognized that natural toxicants need to be better identified within this mode of production. Environmental and food processing contaminants are present in both organic and conventional products. It is recommended to improve the monitoring programmes by paying more attention to the mode of production as well as to the whole array of relevant contaminants. (c) 2004 Elsevier Ltd. All rights reserved.