The isolation of a pure sesquiterpene hydrocarbon from the natural coating of Granny Smith apples is described. Evidence mainly from its ultraviolet, infrared, mass, and N.M.R. spectra establish it as an α- farnesene stereoisomer (I) with a trans configuration assigned to the 9,10 double bond and a likely trans configuration of the 6,7 bond. Its infrared, mass, and N.M.R. spectra and those of trans-β-farnesene (II) are reported.