The changing nature of the pollution climate in the second half of the 20th Century has resulted in the increased importance of ozone and nitrogen pollutants and a decreased importance of sulphur dioxide. However, there have been few studies of the effects of any dry deposited gas on individual bryophyte species or on bryophyterich plant communities. In those studies which have been made, there is evidence that well hydrated bryophytes may not be particularly sensitive to ozone or NOx at realistic atmospheric concentrations. Ombrotrophic bryophytes are largely dependent on wet deposition as a source of nitrogen. A good example of the potential latent problem is the increase in total tissue nitrogen concentration in ombrotrophic bryophytes. There is ample evidence to suggest that this is an inevitable and widespread response to enhanced atmospheric nitrogen deposition. The responses of bryophytes to wet atmospheric nitrogen deposition can be examined most readily through studies of nitrate assimilation in near pristine environments.