The aqueous phase behavior of phytantriol (PT) in mixtures of monoolein (MO), distearoylphosphatidylglycerol (DSPG), propylene glycol (PG), polyethylene glycol 400 (PEG 400) and 2-Methyl-2,4-pentanediol (MPD) was investigated by visual inspection, polarized light microscopy and small angle X-ray diffraction at room temperature. The phase diagrams of PT and MO in water are qualitatively very similar and PT/MO mixtures in excess water form one cubic phase of space group Pn3m irrespective of mixing ratio. The addition of the charged membrane lipid DSPG to the PT system gives rise to a considerable water swelling of the cubic phases as well as the occurrence of a cubic phase of space group lm3m. Whereas all three solvents studied give rise to a sponge (L-3) phase in the MO-water system, this phase was only found when MPD was added to the PT-water system. The results are discussed with respect to the chemical differences between PT and MO. (C) 2007 Elsevier Inc. All rights reserved.