A field survey was performed in eastern Finland, where measured ambient SO 2 concentrations were 1.4-3.8 μg m - 3 a - 1 and bulk S deposition 0.17-0.32 g m - 2 a - 1 in 1991-1993. The accumulation of sulphur (S) in needles of Scots pine (Pinus sylvestris L.) was studied with XRF, IC and FESEM analyses and the needle damage examined under a light microscope and by SEM. Foliar N concentrations were also measured. Foliar total S concentrations were observed to be above the normal S level (500-700 μg g - 1 ) over almost the whole area. Slight chlorosis and/or necrosis of the needle tips and stomatal areas, changes in the needle surface waxes and localization of S into needle tips and mesophyll cells around the stomata suggested the impact of S deposition, as did the calculations of S t /N t , and predicted and excess S. A concentration of about 900 μg g - 1 may be considered a critical level for foliar S t in areas with low N supply.