The biospheric part of the anthropogenic sulphur cycle was investigated in a heavily polluted area at the northern slope of the Karkonosze Mountains, SW Poland. Norway spruce (Picea abies) needles, from a 900 m vertical transect (400 to 1300 m above sea level), were collected on two consecutive days of spring 1998 and one day of winter 1999. Concentrations of sulphate sulphur (SO42-), and organic sulphur (Sorg)n and isotope ratios of organic sulphur and sulphate from spruce needles have been analyzed. (SO42-)n and (Sorg)n were rather constant and δ34S(SO42-)n and δ34S(Sorg)n values increased with higher altitude. This is attributed to an increase in atmospheric SO2 concentration and light intensity, which enhance emission of 34S-depleted hydrogen sulphide (H2S) from needles. The δ18O(SO42-)n decreases with altitude due to the altitudinal 18O-depletion of atmospheric precipitation and increased formation of needle sulphate from atmospheric SO2. The isotope effect related to a reduction process during spring can also be seen at higher altitudes by a negative correlation between δ18O(SO42-)n versus (SO42-)n and δ34S(SO42-)n versus (SO42-)n of spring needles. Winter needles show an opposite trend of potential oxidation of the SO2 assimilated. The Δ34S(SO42- - Sorg)n value shows a very good correlation to the abundance of dust on needles. Higher abundances of dust may limit foliar gas exchange and thus higher Δ34S(SO42- - Sorg)n values reflect conditions which are closer to sulphur isotope equilibrium in the sulphate-organic sulphur system, whereas lower Δ34S(SO42- - Sorg)n values characterize a higher gas exchange rate and more dynamic conditions for the sulphur system in needles. Hydrogen sulphide emission is the most likely mechanism to control variations in the observed δ-values, and dust abundance may control variations in the Δ-values.