Increases in N deposition (wet and dry) have been associated with a decline in seminatural plant communities, adapted for growth on nutrient poor soils in the UK and Europe. The impacts of N deposition applied as either wet NH4+ or gaseous NH3 on vegetation (7 species) from acid moorland in SE Scotland were compared in a dose-response study. Wet N deposition at 0, 8, 16, 32, 64, 128 kg N ha-1 y-1 was applied as NH4C1, and dry deposition as gaseous NH3 (2, 6, 20, 50, 90 μg NH3 m-3) under controlled conditions in open-top chambers. A strong linear doseresponse relationship (p<0.05) was found between foliar N content in all seven plant species and applied NH4-N. However, in the NH3 treatment, only C. vulgaris and P. commune showed a significant response to increasing N additions. NH3 was found to increase the rate of water loss in Calluna in both autumn and winter by comparison with wet deposition. For Eriophorum vaginatum, the NH3 and NH4+ treatments showed significant N dose response relationships for biomass. A significant increase in above ground biomass, proportional to the added N, was found for Narthecium ossifragum when N was applied as NH3 compared to NH4+.