Seedlings of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), beech (Fagus sylvatica) and ash (Fraxinus excelsior) were exposed to different ozone scenarios ranging from background concentrations to levels characteristic of higher altitudes in the open-top chambers of the Birmensdorf field fumigation facility for one season. No biomass losses were detected in any of the 4 species, but beech and ash developed visible injury symptoms. However, a clear dose/effect relationship was not apparent.