National Monitoring Programme in Sweden. The purpose is to quantify deposition (mainly of sulphur and nitrogen), and to illustrate effects in the soil, for example possible acidification. The aim of the network is to describe the current situation, regional differences, trends over time, and the effects of acid deposition. The atmospheric deposition of sulphur and nitrogen are the main causes of current acidification of ecosystems. Acidification results in substantial pH reduction in soil, groundwater, lakes and water courses. Deposition is investigated as precipitation studies in open field areas (bulk precipitation) and by throughfall studies in nearby forest stands. For sulphur and chloride, throughfall monitoring is useful for determination of total deposition. In areas, or during periods with low sulphur deposition, internal circulation in vegetation might influence results from throughfall measurements significantly. For nitrogen and base cations (mainly potassium and manganese) canopy interaction is important. Air concentrations of sulphur and nitrogen dioxide, ammonia, and ozone are measured at some locations. The observations made are: (i) air chemistry (SO2, NO2, NH3, O3); (ii) soil water chemistry (pH, Alk, SO4-S, Cl, NO3-N, NH4-N, Ca, Mg, Na, K, Mn, Fe, ooAl, oAl, Al-tot, total organic carbon); (iii) deposition in open field (precipitation, H+, SO4-S, Cl, NO3-N, NH4-N, Ca, Mg, Na, K, Mn); (iv) deposition in forest (throughfall, H+, SO4-S, Cl, NO3-N, NH4-N, Ca, Mg, Na, K, Mn). For nitrogen and base cations (mainly potassium and manganese) canopy interaction is important. Soil solution chemistry in the forest stands is used as indicator of soil conditions.