The debate over chlorine in industrialized economies has become extremely polarized in the last decade. Environmental pressure groups are striving for a virtual phaseout of chlorine and chlorinated hydrocarbons (CHCs), because they are convinced that the risks cannot be managed. Industry argues this is not necessary because environmental risks can be controlled, nor is it feasible, because at least 60% of all firms use CHCs, produds made with CHCs, or elemental chlorine. In an attempt to give this discussion a more factual basis, the Dutch minister of environment launched a strategic study on chlorine (see Kleijn et al. I997;Tukker et al. 1995). Using all available knowledge about emissions and contemporary evaluation methods, the study found only a limited number of environmental issues outstanding related to the chlorine chain: however, it also found important uncertainties. This article describes the outstanding uncertainties in more detail. It defines which uncertainties have to be regarded as chlorine‐specific and the extent to which additional research can resolve them. For the remaining uncertainties the potential benefts of uncertainty reduction strategies are evaluted, relying mainly on the precautionary principle