This Occasional Paper describes the damage caused by the green spruce aphid, Elatobium abietinum, to Sitka spruce growing in Britain. Following an outbreak of this aphid in South Wales in 1980, it was possible to compare the impact and recovery of shoot growth in experimental plots at Rhondda Forest of a IUFRO provenance collection of Sitka spruce from a wide range of North American origins. In all those provenances measured, the mean height growth was less than half that of the previous years and all plots showed a continuous depression of shoot growth for at least two seasons after attack, except those from California. Data on the phenological displacement of plant dormancy and bud break and the associated changes in foliar amino-acid concentration of old needles is presented and the influence this has on aphid population increase is discussed.