Respiration of four decomposer fungi (Mycena galopus (Pers.) Kutnmer, Aureobasidium pullulans (de Bary) Arnaud, Phoma exigua Desm. and Cladosporium cladosporioides (Fres.) de Vries) growing on four species of leaf litter (Pinus sylvestris L., Picea sitchensis (Bongard) Carriére, Fraxinus excelsior L. and Corylus avellana L.) was inhibited by dry-deposited SO2 in a laboratory experiment. Mycelial extension of the four fungi growing on four different agar media was inhibited by SO3 fumigation (40 nl l−1) in the laboratory, and media containing carbohydrates decreased the inhibitory effect of SO2 fumigation. Fumigation caused a statistically significant reduction in the mycelial extension of all species tested on tap-water agar. These experiments demonstrate that decomposition of leaf litter is inhibited by environmentally realistic concentrations of SO2 and that the effect is exerted via inhibition of saprotrophic fungi.