The physical properties of reverse micelles formed by (lecithin + nonpolar solvent + H 2O) systems, where the nonpolar solvent is benzene, carbon tetrachloride, or cyclohexane, have been investigated by optical birefringence, viscosity, light scattering, electrical conductivity, and transmission electron microscopy. A 5% w/v solution of lecithin in any of the above nonpolar solvents solubilizes about 16 mole of water per mole of lecithin. Light-scattering studies reveal that, in the carbon tetrachloride and benzene media, spherical reverse micellar aggregates are formed throughout the range of water concentrations studied, the radii of gyration ( R g) being in the range 400–500 Å for the former system and in the range 500–600 Å for the latter. In the cyclohexane solvent, however, the initial spherical structures that are formed have an R g around 300 Å; further, in this system, formation of an anisotropic phase sets in at a composition of about 6 mole of water per mole of lecithin, leading to elongated (cylindrical or lamellar) aggregates. This phase transition is also clearly revealed in the electrical conductivity measurements performed with added KCl as an indicating electrolyte in the aqueous phase. Electron micrographs offer further support of the above reverse micellar geometries and, for the cyclohexane system, reveal that the anisotropic phase is present in the form of tubular structures containing aqueous canals.