The new prefuranic labdane diterpene 9 α,13 R;15,16-diepoxy-12-oxo-labd-14-en-19,6β-olide (polyodonine) has been isolated from the aerial parts of Marrubium polydon. The known 3-O-(β- d-glucopyranosyl)-3β-hydroxystigmast-5-ene and the flavone glucosides 7-O-[β- d -(6-O-p- coumaroyl)-glucopyranosyl]-apigenin and 7-O-[β- d-(3,6-di -O-p- coumaroyl)-glucopyranosyl]-apigenin were also obtained from the same source. The structure of polydonine has been determined primarily on the basis of NMR spectroscopy.