The volatile oil from two populations of red spruce was found to consist mainly of bornyl acetate (55 per cent). Smaller amounts of α- and β-pinene, camphene, 3-carene, myrcene, limonene, α- and β-phellandrene, p-cymene, 1:8-cineole, linalool, camphor, terpinen-4-ol, α-terpineol, borneol, piperitone, citronellyl and geranyl acetate, bisabolene and a mixture of γ- and δ-cadinene (“canadene”) were also isolated. Santene, tricyclene, γ-terpinene, thujone, isothujone and isoborneol were tentatively identified. The leaf oils of the foliage from black spruce (2 trees) white spruce (3 trees) and Colorado spruce (5 trees) were analysed by GLC and the data obtained were compared with those of red spruce. The close phylogenetic relationship of red and black spruce was found to be reflected in the chemical composition of their leaf oils, whereas significant chemical differences were observed with both white and Colorado spruce. Hypothetical pathways for the formation of the terpenes found in spruce leaf oils from a single precursor, such as geranyl pyrophosphate, are discussed. Piperitone, a C-3 oxygenated monoterpene, appears to take an exceptional position in such postulated sequences. Also, not all of the compounds expected from schemes involving carbonium-ion intermediates are found in the spruce leaf oils.