Gas chromatography and GC/MS were used to identify terpenoids and other volatiles from leaves of rough lemon rootstock seedlings which were grown in soil of three treatments. Treatments were soil low in phosphorus (P), the same soil amended with 440 ppm P, and the low P-soil amended with the mycorrhizal fungusGlomus intraradices(G.i.). Treatments yielded 30, 78, and 81 separate components, respectively. A total of 101 different components were present among the three treatments, and of these, 48 were chemically identified. Nine to ten compounds were unique to each of the treatments. A total of eight sesquiterpenes were present, and plants in the low-P soil amended withG.i.contained the highest relative concentration of sesquiterpene hydrocarbons, 16.06%, followed by 13.82% in plants in the low-P unamended soil and 8.03% in plants in soil amended with P. No single sesquiterpene was an indicator of stress in the stunted nonmycorrhizal plants. The qualitative simplicity of extracts from plants in the low-P unamended soil may be due to impaired phosphate metabolism, since precursors of both mono- and sesquiterpenes contain high-energy phosphate bonds.