In two open, flow-through systems 11 lichen species were fumigated with concentrations between 0·036 and 2·0 ppm (c. 94·3–5240 μg m−3) SO2. Sulphur dioxide uptake was monitored concurrently as a mass balance between incoming and outgoing SO2 concentrations. The rate of uptake ranged from 0·025 (±0·006) to 0·7 (±0·16) nmol SO2 g−1 d. wt s−1, for all species. After the first hour of fumigation the uptake rate was almost constant during the following 5 h for concentrations up to 1·0 ppm SO2. At higher concentrations the uptake declined over time continuously. Within the range of measured SO2 concentrations the uptake rate was linearly correlated with SO2 concentrations (r2=0·90). Thalli which were killed by heat treatment or in which respiration was inhibited by azide treatment did not show significantly different SO2 uptake from living thalli. No differences in uptake were found during fumigation in the light versus in the dark.