Areas which experience prolonged snowlie and possess a distinctive bryophyte-dominated vegetation are termed snowbeds. Snow is a very efficient scavenger of atmospheric pollution. Because of the dynamics of snowmelt, much of the pollutant load of a snowpack is released in a highly concentrated episode known as the ‘acid flush’. This flush is received by the underlying vegetation when it is covered by the snow and also when it has been exposed after snow cover. Concentrations of pollutants which are already occurring in the meltwater of Scottish snowbeds are shown to be causing damage to the underlying bryophytes. Damage is greatest when the pollutants are received by the plants when out of snow cover. Recovery from the damage is slow and in some cases the plants show no signs of recovery 4 wk after exposure to polluted snow meltwater. Given the very short growing season available to the plants, damage persisting for so long could impinge on the plants'potential for survival. The long-term threat to these sensitive communities is a serious one.