Increases in nitrogen deposition over the past 30 years may be causing changes i n vegetation composition in the UK. Three sites were selected for vegetation survey in 1989 and results have been compared with past data. On the Breckland heath sites studied i n East Anglia where gaseous inputs of nitrogen are high, Calluna vulgaris is generally in a degenerate phase and regeneration is poor. Areas are becoming increasingly grassy and Deschampsia flexuosa cover is increasing. Nitrogen concentrations in foliage tend to be high compared with other sites. The evidence suggests that increased nitrogen deposition is implicated in the decline in Calluna vulgaris at some sites , its susceptibility to catastrophic events and possible successional change to grassland. At Inverpolly, Ross-shire, limitations i n experimental design preclude firm conclusions but changes observed do not entirely conform with changes in grazing pressure at the site and increased atmospheric input of nitrogen particularly at high elevation sites could be affecting vegetation composition. Changes in nitrogen content of foliage during the past 20-30 years is being examined by comparing content of herbarium bryophyte material with content of current samples collected from the original locations. Initial results from a survey of nitrogen content of Calluna vulgaris in the UK indicate that concentrations of nitrogen tend to reflect the pollution climate of the site. In experimental studies. Calluna vulgaris turfs and Eriophorum vaginatum tillers are being exposed to mist treatments of varying nitrogen concentration in open-top chambers. Preliminary results suggest a positive growth response to the highest nitrogen treatment in both experiments.