The spasmolytic activity of a flavonoid fraction of a commercial sample of yarrow (Achillea millefolium s.l.), its main flavonoids as well as quercetin and two flavonoid metabolites were investigated on isolated terminal guinea-pig ilea. The aglycones quercetin, luteolin and apigenin exhibited the highest antispasmodic activities with IC50 values of 7.8 micromol/L, 9.8 micromol/L and 12.5 micromol/L, respectively. Rutin and the flavonoid metabolites homoprotocatechuic acid and homovanillic acid showed no significant effects on contractility of the terminal ilea. From the results on the spasmolytic activity of the flavonoid fraction, the glycosides and the respective aglycones it is concluded that in tea prepared from yarrow the concentration of the flavonoids is high enough to exert a spasmolytic effect in the gut, which is mainly caused by blockade of the calcium inward current, but additionally also by mediator-antagonistic effects.