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The disaccharides, sucrose and trehalose, markedly decreased (up to 17-13C°) the temperature of the lamellar to hexagonal (L_α →H_II) phase transition and simultaneously increase by 2–4 C° the temperature of the lamellar gel to lamellar liquid-crystal (L_β →L_α) phase transition in hydrated dihexadecylphosphatidylethanolamine and distearoylphosphatidylethanolamine. These two transitions merge and convert into a single L_β-H_II phase transition when dispersed in 2.4 M sucrose. These results are inconsistent with recent reports by 8, 9) which suggest that trehalose stabilizes the L_α phase relative to the H_II phase and shifts upwards beyond detectability the L_α-H_II transition. The present results are considered as a manifestation of the Hofmeister effect in which the sugars act as kosmotropic reagents stabilizing the structure of bulk water. This tends to decrease the area of contact between the lipid and the aqueous …