The morphology of the hybrid bicelles was directly observed with cryogenic transmission electron microscopy (Cryo-TEM), enabling in situ visualization of supramolecular assemblies in water. We observed ellipsoidal and rod-like objects corres- ponding to the projections of face-on and edge-on bicelles, respectively (Fig. 2). Upon tilting the sample holder 201, a number of circular features became rod-shaped and vice versa, demonstrating the discoid structure of the bicelles.11 The average radius of hybrid bicelles, determined by analysis of 50 samples, was 20 nm (S.D. = 5 nm), which is in good agreement with a previous report on phospholipid bicelles consisting of 1,2-dipalmitoyl-sn-glycero-3-phospho-choline (DPPC), which has hydrophobic chains with the same length as 1, and 2 (7 : 2 molar ratio).4 Since the edge-on bicelles displayed thicknesses of 4.4