A number of lignans, including those isolated from Arctium lappa (Compositae), were subjected to Ca²⁺ antagonist assay. The most potent activity occurred in trachelogenin, the calculated Ic50 and pA₂ of which were 1.1×10^-6 M and 6.60 respectively. Tranchelogenin had a potent and long-lasting antihypertensive effect on spontaneously hypertensive rats.