Quercetagetin 3'-methylether- 7-O- β - D-glucopiranoside (MQ), isolated from the flowers of Centaurea rupestris L. is flavonoid known to possess antiphytoviral activity. The aim of this study was to test: the flavonoid content in leaves, flowers and roots of naturally-growing C. rupestris and in vitro grown undifferentiated, differentiated and transformed tissues ; the antiviral activity of tissue extracts against tomato bushy stunt virus. In vitro grown tissues (shoots ; embriogenic callus-EC ; tissue consisting of callus and shoots ; transformed roots) were propagated on nutrient medium with different combinations of plant growth regulators. The highest content of total flavonoids, including MQ, was detected in extracts of naturally-growing leaves and flowers. These extracts showed strong antiviral activity. Although the concentration of MQ was the highest in flowers, leaf extract showed stronger antiviral activity. MQ was detected in all differentiated in vitro grown tissues including transformed roots in which the concentration of MQ was significantly higher than in naturally– growing roots. The fact that antiviral activity of tissue extracts did not directly correlate with the concentration of MQ prompted us to search for other substances that might have contributed to this activity. Luteolin, one of the possible precursors of MQ was found in all tissues except in EC. Caffeic as well as coumaric acid, a direct precursor of caffeic acid and an early precursor of a number of flavonoids, were detected in all investigated tissues and their antiviral activity was confirmed.