Abstract Wild Mentha spicata plants from 3 locations on the Island of Zakynthos had essential oil yields (mL/100g DW) ranging from 0.5â1.1 %. The main oil constituents were trans-piperitone oxide, piperitenone oxide and 1,8-cineole. On a whole plant basis (aerial parts) the trans-piperitone oxide content ranged from 1.4 % location (Loc 1) to 32.5% (Loc 3) and appeared to have an inverse relationship with the 1,8-cineole content which ranged from 10.8 % (Loc 3) to 37.9 % (Loc 1). 1,8-cineole was the major oil constituent (37.9 %) of M. spicata plants from Loc 1. The major constituent of the inflorescence oils was piperitenone oxide which ranged from 32.4 % (Loc 3) to 46.3 % of the oil (Loc 1). The major constituent of the leaf oils was 1,8-cineole (40.5 %) in plants from Loc 1 and trans-piperitone oxide in plants from Loc 2 (19.8 %) and Loc 3 (33.5 %). This is the first report for wild populations in Greece of a M. spicata oil in which 1,8-cineole is the major constituent. The observed variation in essential oil composition between locations and plant organs in July would not appear to be directly related to the climatic conditions. Key Word Index: Mentha spicata Lamiaceaeessential oil composition trans-piperitone oxidepiperitenone oxide1,8-cineole