The essential oils from the aerial parts of Prasium majus (Labiatae), collected in two phenological stages in Greece, were analysed by GC-MS. Thirty-two compounds were identified, representing 99.8-99.9% of the total oils. The major constituents in sample A were 1-octen-3-ol (20.7%), α α α α α-pinene (14.7%) and linalool (13.8%), while those of sample B were dehydro-aromadendrene (31.8%), caryophyllene oxide (13.7%) and 1-octen-3-ol (12.4%).