Thirty nine flavonoids, isolated from plants, were tested in respect of their influence on soybean lipoxygenase activity, cyclooxygenase activity and inhibition of ascorbic acid-stimulated malonaldehyde formation in liver lipids. Almost all of the tested compounds were antioxidants and stimulated cyclooxygenase when arachidonic acid was used as a substrate at a concentration of 100 microM. Eleven flavonoids were inhibitors of soybean lipoxygenase. A good correlation between the chemical structure and the tested activity was observed. The most active compounds in all tests were luteolin, 6-hydroxyluteolin, nepetin, quercetagetin, patuletin and myricetin.