In this study an assessment has been made of the present and possible future acidification and eutrophication of natural and semi-natural terrestrial ecosystems, and riverine nitrogen transport to estuaries, coastal seas and continental shelves. The major objectives were to delineate areas potentially affected by depostition of nitrogen and sulphur compounds, to estimate the severity of acidification and eutrophication problems, and to identify research and data gaps. The results indicate that the critical loads for acidification and eutrophication are exceeded in 6-15% and 7-18% of the global area of natural and semi-natural ecosystems, respectively. Currently, most serious risks are found in the heavily industrialised regions of eastern USA, Europe and the Former Soviet Union, but risks were also found for parts of South America, large parts of ASIA and parts of Western, Eastern and Southern Africa. Scenario analysis shows that both acidification and eutrophication risks could significantly increase in the second group of regions.