The MeOH extract of the dried root tubers of Polygonum multiflorum yielded three bioactive compounds with an inhibitory activity on calmodulin-depleted erythrocyte calcium-dependent ATPase. These compounds were identified as E-2,3,5,4'-tetrahydroxystilbene 2-O-beta-D-glucopyranoside [2] (IC50 = 240 microM) and cis- and trans-E-3-butylidene-4,5,6,7-tetrahydro-6,7-dihydroxy-1(3H)- isobenzofuranone [3 and 4](IC50 = 160 and 260 microM, respectively). E-2,4,6,4'-Tetrahydroxystilbene 2-O-beta-D-glucopyranoside [1] was also isolated but was found to have no inhibitory effect on the enzyme.