TLC investigation of the flavonoid fraction of Chenopodium murale L. revealed the presence of three components. The major was identified as kaempferol-3,7-dirhamnoside 1 (kaempferitrin; lespedin) through its MP, UV, IR, MS and NMR (H-H COSY and H-C. HECTOR) spectra. Testing the effect of compound 1 as well as the total flavonoid mixture on the rabbit cardiovascular system, showed dose-related hypotension and bradycardia. Compound 1 also produced a dose-related hypotension in genetically prone hypertensive rats. Compound 1 did not block a1 or b1-adrenoceptors when tested using isolated guinea-pig aoric strip and atria, respectively. Quantification of 1 in C. ambrosoides, C. murale, C. ficifolium and C. album revealed that the former contains the highest level.