In this study the rate of growth of ash (Fraxinus excelsior L.) on a variety of sites in the English Lake District is related to the chemical composition of the foliage. The foliar composition reflects the nutrition of the trees and explanation of this varying composition is sought from site factors including soil description and analysis. The foliar composition may itself influence soil conditions. While there are several studies, some silvicultural and some ecological, which reflect some part of this complex relationship, the range of natural or at least naturally regenerated ash sites available for study in the Lake District has made it possible to follow this theme right through. The response of several species of Fraxinus and other deciduous tree seedlings, in nurseries and pot experiments, to various pH levels, manures and fertilizers, particularly nitrogen, phosphorus and potassium, is widely reported in several countries (e.g. Weis 1927; Treschow 1934; Bornebusch 1941; McComb & Kapel 1942; Wardle 1961). Two studies, both in plantations, have related nutrient uptake, particularly nitrogen, to growth and plantation success of white and green ash and other hardwoods in the Lake States (Wallihan 1949) and Iowa (Hansen & McComb 1958). Also Mitchell & Chandler (1939) compared the response in current diameter growth of different North American hardwood stands to nitrogenous fertilizers. Apart from the work of Tamm (1956, 1957) and Viro (1950, 1951) there has been little work in Europe on the growth of naturally regenerated stands in relation to their nutrition. The work of Ovington & Madgwick (1959) on birch in Holme Fen Nature Reserve deals more with productivity and the nutrient cycle than with growth and nutrition. The nutritional studies of Leyton (1954, 1956, 1957), VanGoor (1954) and Wright (1959) on nutrition as related to growth have mainly been confined to the somewhat artificial conditions found in plantations. Also there are numerous accounts, especially from the United States, which relate growth to edaphic site factors. This work must also be seen against the background of several accounts of different aspects of the ecology of F. excelsior in Britain (e.g. Chinner 1948; Zehetmayr 1947; Brown 1950; Weston 1951; Mahendra 1952; Majid 1954; Moseni 1954). Wardle (1959) has presented data on the establishment and survival of regeneration, as affected by a succession of predators and parasites, and the growth rates, as influenced by light intensity, of seedling ash in competition with Mercurialis. Also Wardle (1961) has summarized much information on Fraxinus excelsior in the Biological Flora of the British