Spartium junceum L. (Fabaceae) flowers are used for the treatment of peptic ulcers in Turkish folk medicine. The possible superoxide dismutase-like activity of the extracts, fractions and constituents obtained through activity-guided fractionation were studied by using in vitro electron spin resonance spectrometry, in order to explain the role of antioxidant principles in the potent antiulcerogenic activity of the extract. Despite the fact that the triterpene, spartitrioside, which was previously reported as the active antiulcerogenic constituent of the flowers was found almost inactive, the flavonoid-rich fractions showed potent antioxidant activity. Five flavonoid glycosides bearing catechol structure in ring B were isolated from the butanol extract and their structures were elucidated using (1)H- and (13)C-NMR techniques as isoquercitrin (quercetin 3 beta -glucoside) (1,); luteolin 4'beta -glucoside (2); quercetin 3, 4'-diglucoside (3); azaleatin 3 beta -glucoside (quercetin 5-methylether 3 beta -glucoside) (4), quercetin 4'beta -glucoside (5). Flavonoids (2) and (4) showed the highest in vitro antioxidant activity with 22.59 and 19.08 U/ml, respectively. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.