The inhibition of Na+,K(+)-ATPase activity by various constituents of Moutan Cortex and Paeoniae Radix was studied. 1,2,3,4,6-Penta-O-galloyl-beta-D-glucose (PGG), a major component of both crude drugs, strongly inhibited Na+,K(+)-ATPase activity (IC50 = 2.5 x 10(-6) M), whereas galloylpaeoniflorin,