Germany was the first country to introduce occupational exposure limits (OEL) in 1886. A theoretical consideration for the existence of toxicological thresholds has been provided. Prerequisites for OELs are seen in: reversibility, existence of a threshold, deviation of (physiological) functions from normal to be regarded as "safe", knowledge about mechanism of toxic effect; and for the decision process: complete transparency of decision making, and combination with intensive health surveillance in the workplace. A variety of additional provisions has been introduced into the German MAK-list: a system for limitation of peak exposures; notification of sensitization and skin absorption, and of reproductive hazards; no satisfactory regulation of exposure to mixtures has been established. Occupational carcinogens constitute a special case because of identification of a threshold and the establishment of health-based standards has not yet been demonstrated justifiably. At present, strategies are elaborated for the quantification of cancer risk from a given compound. Despite many shortcomings and criticism. OELs continue to be an important and valid instrument for the protection of workers' health.