The neutral, volatile oil of the foliage of western red cedar was analysed by means of gas-liquid chromatography and infrared spectroscopy. The major constituent was found to be l-thujone accompanied by nearly 10 per cent d-isothujone. The main hydrocarbons were d-sabinene and tentatively identified car-4-ene. Smaller amounts of d-α-pinene, d-limonene, d-terpinen-4-ol and an unidentified aromatic ester were also isolated. Trace amounts of α-fenchene, camphene, γ-terpinene, terpinolene, p-cymene and 1,8-cineole were identified by retention characteristics only. The presence of thujyl alcohol and its acetate could not be confirmed. The oil from small branchlets from different locations on a young tree was analyzed separately. The qualitative composition was found to be the same, but the younger leaves contained a noticeably smaller amount of hydrocarbons than older ones. The oil may lend itself to a study of the biosynthesis of some of its components and possible pathways are discussed.