An eighteen-year-old clone of Sitka spruce ( Picea sitchensis (Bong.) Carr) growing in the field was used to evaluate the whole tree response of ‘mature’ Sitka spruce to acid mist treatment. The mist, an equimolar mixture of H 2SO 4 and NH 4NO 3 at pH 2.5 with or without particles (soda glass ballotini < 20 μm diameter), was applied twice weekly (equivalent to 4 mm precipitation week −1) throughout the growing season, May–November 1990–1992. The annual dose of S, N, H applied as mist (at 51, 48 and 3.3 kg ha −1, respectively) was 2.5 times that measured in the Scottish uplands. Throughout the experiment there was no evidence of visible injury symptoms, yet there was a highly significant reduction (p < 0.02) in the stem-area increment relative to the stem area at the start, measured using vernier dendrometer bands. There was no significant difference between the (acid mist + particle) and the acid mist only treatments. The mean relative stem-area increment over two complete growing seasons (1991–1992) was 65% for control trees, but only 53% for acid-misted trees.