Structures of aqueous dispersions prepared from monoglycosyldiglycerides and from mixtures of monoglycosyldiglyceride and phosphatidylcholine were studied by freeze-fracture electron microscopy. Aqueous dispersions of glucosyl or galactosyl dipalmitylglycerol formed lamellar structures when quenched both from below and above the gel-liquid crystalline phase transition temperature. With mixtures of monoglycosyl dipalmitylglycerol and dipalmitoylphosphatidylcholine, tubular structures could be observed in the extended bilayer structures. Diglucosyl dipalmitylglycerols showed only a smooth fracture surface, however, when mixed with dipalmitoylphosphatidylcholine. In the fractured face of dispersions composed of egg yolk phosphatidylcholine and glucosyl dipalmitylglycerol, particles having a diameter of 3-6 nm, instead of tubular structures, were observed, suggesting that the occurrence of tubular structure may depend on the fatty acid compositions of the mixtures. A mixture of dipalmitoylphosphatidylcholine and galactosylceramide did not show any distinct tubular or globular structures on the fractured face. These findings indicate that structure in the polar group of molecules as well as structure in the non-polar group may be important for the formation of a non-bilayer, tubular structure.