Five environmental problems have been identified, which should see significant improvement in the United Kingdom, if action is taken within the United Nations Economic Commission for Europe (UN ECE) Second NO(x) Protocol to control NO(x) emissions. These problems are: acidification and eutrophication of soil ecosystems; episodic peak ozone and human health; ozone damage to crops and forest trees; wintertime NO₂ pollution episodes and summertime fine particulate formation and human health. There are a range of environmental and health thresholds that can be used as a guide to setting NO(x) emission reduction targets for these problems within the proposed Second NO(x) Protocol. It is recognized, however, that achieving some of these targets will require actions beyond those regarded as feasible even if their desirability is acknowledged. These targets can at least provide bench marks against which agreed reductions can be assessed, within the context of a multi-pollutant multi-effect framework to the proposed Second NO(x) Protocol.