Acaciaside A and B, two acylated triterpenoid bisglycosides isolated from the funicles of Acacia auriculiformis, are known to have antihelmintic activity. Since the saponins contain a conjugated unsaturated system that is highly susceptible to peroxidation, we investigated the interaction of saponins and membrane using rat liver microsomes as our model. Microsomal membranes were incubated with saponins at 30 degrees C for 2 hr. Following incubation, lipid peroxidation was measured in terms of malondialdehyde and conjugated diene. Our results showed that incubation of microsomal membranes with saponins increased both malondialdehyde and conjugated diene. The results suggest that in our model, saponins enhance the membrane lipid peroxidation.