The phase behaviors of dipalmitoylphosphatidylethanolamine (DPPE) dispersed in dimethyl sulfoxide (DMSO) aqueous solutions were studied by using differential scanning calorimetry and X-ray diffraction methods. At low concentration of DMSO (mole fraction, x < 0.2), phase transition between lamellar-gel and lamellar liquid-crystal phase can be observed during heating/cooling cycles at a scanning rate of 5&DEG;C min(-1). The formation of the stable lamellar-crystal phase from the metastable lamellar-gel phase needs long time incubation. At moderate concentration of DMSO (0.2 < x < 0.37), phase transition from lamellar-gel to crystalline phase can be detected during either cooling or heating at the same scanning rate. At high concentrations (x > 0.37), DMSO promotes remarkably the formation of lamellar-crystal phase of the lipid, resulting in phase transitions between lamellar-crystal phase and liquid-crystal phase during heating/cooling cycling. A phase diagram has been constructed over the entire concentration range of the mixed solvent. In addition, it was found that DMSO could decrease the lamellar repeat spacing of crystalline and liquid crystalline phase. (C) 2003 Elsevier B.V All rights reserved.