The effects of 15 jatrophane diterpene polyesters (1-3 and 5-16) isolated from lipophilic extracts of Euphorbia serrulata, E. esula, E. salicifolia, and E. peplus (Euphorbiaceae) on the reversion of multidrug resistance of mouse lymphoma cells were examined. The structures of five new compounds (1-5) were elucidated by spectroscopic methods, including HRFABMS, ESIMS, (1)H-(1)H homonuclear and (1)H-(13)C heteronuclear correlations, long-range correlation spectra, and NOESY experiments. The stereochemistry and absolute configuration of one compound (3) were determined by X-ray crystallography. The structure-activity relationship is discussed.