A comparative study of antioxidant (radical-interceptor) properties of tryptanthrin (quinazoline alkaloid shows a high anti-inflammatory activity and it is found in many types of different families of higher plants and microorganisms, including the human microbiome) in the systems of 2,2'-azo-bis(2-methylpropionamidin)dihydrochloride-luminol and hemoglobin-hydrogen peroxide-luminol has been conducted and the influence on the permeability of planar bilayer lipid membranes is evaluated. Trolox was used as a reference antioxidant, and ascorbic acid and dihydroquercetin were taken as standards. Tryptanthrin exhibits very weak antioxidant activity, being markedly inferior to the reference standard and antioxidants while testing antioxidant activity in both studied systems. By the efficacy of antioxidative action the substrates in the systems studied can be arranged in the following order: dihydroquercetin > trolox > ascorbic acid > tryptanthrin. Antioxidant potential of tryptanthrin is approximately 1000 and 3000 times lower than that of trolox and bioflavonoid dihydroquercetine, respectively. Tryptanthrin causes no significant changes in the permeability of planar bilayer membranes in a dose range of 0.5 to. 10 μg/ml. Our data show that tryptanthrin displays no significant radical-interceptor and membranotropic activities. It can be assumed that the observed high anti-inflammatory activity of tryptanthrin is not related to the neutralizing effect against reactive oxygen species and the influence on the permeability of cell membranes. The anticipated mechanisms of biological activity of tryptanthrin are discussed.