A methanolic extract of the aerial parts of Salvia candelabrum was subjected to multiple chromatographic separation under the guidance of anti-lipid peroxidation assay. From the most active fractions seven abietane and seco-abietane diterpenes were isolated by preparative TLC purification. Besides candesalvoquinone, candelabroquinone, 12- O-methylcandesalvone B, candesalvone B methyl ester and candelabrone (all reported earlier), the known candesalvone B and the new candesalvolactone were identified. The structures were established by means of mass spectroscopy and advanced 2D NMR methods. All the identified compounds were evaluated for antioxidant activity in enzyme-dependent (IC (50) values 3.49 - 10.42 microM) and enzyme-independent (IC (50) values 1.40 - 13.40 microM) systems of lipid peroxidation. All compounds displayed marked concentration-dependent effects in both tests as compared with those of authentic ascorbic, rosmarinic and caffeic acids. The differences in antioxidant capacities observed in the enzyme-independent system allowed conclusions concerning structure-activity relationships.