In spite of the close botanical analogy with Marrubium vulgare, Marrubium incanum (collected in Jugoslavia) contains only a very small quantity of marrubiin. After chromatography of the acetone extract on silica-gel we isolated, together with small quantities of other diterpenoids and several flavanoids, a crystalline substance (I). C20H2605, m.p. 172-173, [a]: +480 (c=l% in CH OH), 3 x max 212 ml (~=10300), 290 mp (~<100), as the most abundant terpenoid constituent. The physical properties of I correspond with those described by L. A. Salei, D.P. Popa and G. V. Lazur'evskiy (1) for peregrinine, a compound isolated from Marrubium peregrinum, which possesses the same molecular formula but whose structure has not been elucidated. The spectral features of compound I were: vma -zf (KBr) 3597 (strong), 3560 (weak), 1780 (strong, broad), 1710 (weak), 875 cm ; N.M.R. 0,95 (3H, d, J=6 cps, :CH-Cg3). 7,04 (3H, s, 1,C-CH3), 1,28 (3H, s, sC-Cg3), 4,70 (lH, poorly resolved triplet, multiplet width lo-12 cps), 6,23, 7,21, 7.32 (lH, m, HP, H , Ha furan); a M.S. 346, 328, 302, 95, 94, 81. The I.R., N.M.R., U.V. and Mass spectra indicated the presence of a S-substituted furan in the molecule, and this was also confirmed by a purple colour in the Ehrlich test. The hydroxyl group of compound I resists both acetylation with acetic anhydride in pyridine at room temperature and oxidation with chromic anhydride in pyridine. Oxidation of I with Jones reagent (2) at O over a period of 2h yielded the maleic anhydride (II), C20H2407, m.p. 193-196O, vmax (CHC13) 3600, 1838, 1779, 1761, 1710, 1639 cm. The presence of a y-lactone group in I, indicated by an absorption band at