Abrupt, long-term growth reductions evident in annual ring sequences were visually identified and dated. The simple method used allowed relationship of the frequency of such reductions to site and industry. In the Valais, the first damage occured as early as 1921, with the greatest damage concentrated in the early seventies. From 1977 onwards, recovery is apparent in annual ring sequences from the Valais but not from the Swiss Mittelland. No clear relationships between abrupt growth reduction and site or climate were found. Annual ring analysis indicates local and regional pollution as the cause of the reductions.