A new bisbenzylisoquinoline alkaloid, cissampentin, has been isolated from the aerial parts of Cissampelos fasciculata. Detailed interpretation of various spectra allowed identification of most structural features, including a rare methyleneoxy bridge. Although attempted methylation of this alkaloid led to complex mixtures, reaction with diethyl phosphorochloridate gave a single diethyl phosphate derivative and allowed assignment of a 7'-11 ether linkage. Bioassays indicate significant activity as a repellent to the leafcutter ant Acromyrmex octospinosus, and limited antifungal activity.