The crude root-peel extract of Flemingia vestita, containing genistein as the major isoflavone, has a vermifugal/vermicidal effect. It acts by causing flaccid paralysis accompanied by alterations in the activities of several tegumental enzymes and other metabolic activities in the fowl tapeworm, Raillietina echinobothrida. To elucidate the mode of action of the putative phytochemicals on energy metabolism, crude root-peel extract, pure genistein and praziquantel were tested on glucose 6-phosphate dehydrogenase (G6PDH) and enzymes of gluconeogenesis--pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK) and fructose 1,6-bisphosphatase (FBPase)--in R. echinobothrida. The activities of G6PDH, PEPCK and FBPase were largely restricted to the cytosolic fraction, while PC was confined to the mitochondrial fraction. Following treatments, the G6PDH activity was decreased by 23-31%, whereas the activities of PC and PEPCK were increased by 32-44% and 44-49%, respectively. There was no significant effect by any of the treatments on FBPase activity. We hypothesize that the phytochemicals from F. vestita, genistein in particular, influence the key enzymes of these pathways, which is perhaps a function of high energy demand of the parasite under anthelmintic stress.