In order to characterize the chemical change of the constituents during the processing of Hydrangeae Dulcis Folium, quantitative analyses of phyllodulcin, hydrangenol, and their 8-O-glucosides were developed by means of high performance liquid chromatography. As an application of this HPLC method, the distribution of those dihydroisocoumarins in different parts of Hydrangea macrophylla var. thunbergii was investigated. It was found that these dihydroisocoumarins were contained at the highest concentration in the leaves. Furthermore, the seasonal fluctuation of these compounds in the leaves, together with the height of the plant and total dry weight of the leaves, were clarified and so that, the suitable period for the harvest of Hydrangea macrophylla var. thunbergii was deduced to be from Oct. to Nov.
