Do occupational exposure limits really protect workers from chemical hazards? This text gives an in-depth analysis of three sets of exposure limits: the ACGIH list from the United States, which has a world-wide influence; and the official lists of Germany and Sweden, which are both unusually well-documented. A detailed study of the extensive toxicological documentation offered for these lists makes it possible to calculate the safety margins implicit in the exposure limits. The author finds that the outcome of this analysis is disquieting. Even for the Swedish list, which has the lowest values in the Western world, safety margins are often small or non-existent. He proposes new ways to organize exposure limits and to evaluate toxicological data for regulatory purposes.;The text is intended for policy makers, occupational and environmental health specialists and toxicologists.