Chemical and biological characteristics of stream water quality have been monitored since 1984 in 17 headwater streams in the Cairngorm region of Scotland. Three streams are acidified. (mean pH 6.0), 10 are acid-sensitive (pH 6.8) and a further four are well-buffered (pH 6.8). The acidified streams have impoverished macroinvertebrate faunas. All streams have exhibited a decline in non-marine sulphate concentrations over the last decade in response to reduced sulphur deposition. In the more acidic and acid-sensitive systems this has been matched by a corresponding increase in ANC. Although there is also evidence of an increase in the pH of the most acidic streams, no increased diversity or abundance of acid-sensitive macroinvertebrate taxa have been observed. Further reductions in deposition and longer time for the reversal of soil acidification appear necessary for greater biotic recovery to occur.