Flavonoids are benzo-gamma-pyrone derivatives of plant origin. They possess wide spectrum of biological activity. From the therapeutical point of view the most important are their antioxidant properties. These are the result of high propensity to electron transfer, ferrous ions chelating activity and direct scavenging of reactive oxygen species. Flavonoids inhibit enormous number of enzymes. From the pharmacological point of view inhibition of cyclooxygenase and lipoxygenases as well as scavenging of superoxide anions seem to be essential. Flavonoids are antiinflammatory agents as the result of diminished formation of proinflammatory mediators (prostaglandins, leukotrienes, reactive oxygen species, nitric oxide). They are also antithrombotic owing to their ability to scavenge superoxide anions. These anions are strong inhibitors of prostacyclin production. Removal of superoxide anions by flavonoids facilitates antiaggregatory PGI2 formation. Superoxide anions generate proagregatory isoprostanes. The antiaggregatory effect of flavonoids may be due to the limitation of formation of isoprostanes. Empirical use of flavonoids as drugs acquired recently scientific confirmation.