[en] Spiraeoside (quercetin-4'-glucoside) is the major and most caharacteristic flavonoid of Filipendula ulmaria flowers and is not found in the leaves and stems. This paper describes a quantification of spiraeoside by HPTLC densitometry after derivatization with diphenylboric acid -2-aminoester. The fluorescence of this flavonoid was measured at 330 nm. the spiraeoside content in batches of Filipendula ulmaria flowers ranged from 3 to 4.3 %. It is of note that these results are similar to those published elsewhere after HPLC analysis of other batches.