Licorice root traditionally used as an anti-inflammatory drug exhibited an inhibitory effect on lysoPAF (platelet-activating factor) acetyltransferase in vitro: the ether soluble fraction of the crude drug produced a 27.3% inhibition at a concentration 10 microg/ml. From this fraction, licoricidin (1), 1-methoxyphaseollin (2), 6,8-diprenylgenistein (3) and 1-methoxyphaseollidin (4) were isolated as active components, whose IC50 values were 7.7, 57, 19 and 48 microM, respectively. Licoricidin (1) seems to be one of the most potent compounds of plant origin isolated so far.