In conjunction with monitoring secondary structural changes of Aβ, we detected the incorporation of water molecules into the membrane (Figure ), which strongly suggests the formation of transmembrane structures with water-filled pores or intra-membrane bound water. For antiparallel β-sheet-containing Aβ, the strands are oriented at an average angle of approx. 35° with respect to the membrane normal. This is strongly reminiscent of previous experimental and computational findings, where (antiparallel) oligomeric β-hairpin-based β-barrel and β-sandwich structures have been proposed, which create pores or edges, respectively, that introduce water molecules into the membrane. We also note positive water signals with membranes where incorporation is impossible, this suggests, that even then Aβ attempts incorporation, but only manages to penetrate the upper leaflet. A remaining question is, however, the nature of the transmembrane species composed of parallel β-sheets observed in our spectra. As the number of strands is likely to not be homogeneous, it is possible that growing βhairpin-based β-barrel and β-sandwich structures collapse into parallel structures, which we detect as a sudden change in the spectra.