The stability of a-(1) and /3-asarone (2) in ethanolic solutions (30 %; 100 %; pH 7; pH3) was studied under daylight conditions over a period of six months. After rapid initial light-induced isomerization of 1 to 2, a number of (i) oxidation products, i.e. 2,4,5-trimethoxybenzaldehyde (4); 1-(2,4,5-trimethoxyphenyI) propan-2-one (5); 2,4,5trimethoxypropiophenone (6); and (ii) addition products, i.e. l-ethoxy-l-(2,4,5-trimethoxyphenyl) propane (3); (1 R, 2R; lS, 2S)-l-ethoxy-l-(2,4,5-trimethoxyphenyl) propan-2-01 (7A); (lR, 2s; lS, 2R)-l-ethoxy-l-(2,4,5-trimethoxyphenyl propan-2-01 (7B); (lR, 2R; lS, 2S)-1-(2,4,5-trimethoxyphenyl) propan-l,2-diol (8A); (lR, 2s; 1s 2R)-1-(2,4,5trimethoxyphenyl) propan-1,2-diol (8B); as well as (iii) the dimers 1-(2',4',5'-trimethoxypheny1)-2-methy1-3-(2,4,5-trimethoxypheny1)-1 E-pentene (9) and 1-(2',4',5'-trimethoxyphenyl)-2-methyl-3-ethyIla, 2/3,3a (H)-4,6,7-trimethoxyindane (13) were detected after extractive sample preparation. In addition, three dimers, 1-(2',4',5'-trimethoxyphenyl)-2-methyl-3(2,4,5-trimethoxyphenyl)-penta-1 E, 4-diene (10); 1-(2',4',5'-trimethoxyphenyl)-2-(2,4,5-trimethoxypheny~)-3,4-dimethylcyclobutane (1 1) and 1 -(2',4',5'-trimethoxyphenyl)-2-methyl-3-(2,4,5-tnmethoxyphenyl) prop-1 -en-3-one (12) were tentatively identified. Identifications were carried out by capillary gas chromatography (HRGC) and on-line HRGC techniques, i.e. HRGC-mass spectrometry (HRGC-MS) and HRGC-Fourier transform infrared spectroscopy (HRGC-FTIR) as well as 'H-NMR spectroscopy.