Amyloid beta-peptide (Abeta) is a major component of plaques in Alzheimer's disease, and formation of senile plaques has been suggested to originate from regions of neuronal membrane rich in gangliosides. We analyzed the mode of interaction of Abeta with lipid bilayers by multinuclear NMR using (31)P nuclei. We found that Abeta (1-40) strongly perturbed the bilayer structure of dimyristoylphosphatidylcholine (DMPC), to form a non-lamellar phase (most likely micellar). The ganglioside GM1 potentiated the effect of Abeta (1-40), as viewed from (31)P NMR. The difference of the isotropic peak intensity between DMPC/Abeta and DMPC/GM1/Abeta suggests a specific interaction between Abeta and GM1. We show that in the DMPC/GM1/Abeta system there are three lipid phases, namely a lamellar phase, a hexagonal phase and non-oriented lipids. The latter two phases are induced by the presence of the Abeta peptide, and facilitated by GM1.