The morphology of DMPC/DHPC mixtures at total lipid concentration C-L = 5% (w/w) and DMPC/DHPC ratio q approximate to 3, doped with small amounts of DMPG or CTAB, was investigated. P-31 NMR was used to identify the magnetically aligning phase, and cryo-transmission electron microscopy (cryo-TEM) was employed for structural characterization. Magnetic alignment was found to occur between similar to 30 and similar to 45 degrees C, and cryo-TEM showed that the magnetically aligning phase consisted of extended sheets with a lacelike structure. The aggregates are best described as intermediates between two-dimensional networks of flattened, highly branched, cylindrical micelles and lamellar sheets perforated by large irregular holes. DHPC most likely covers the edges of the holes, while DMPC makes up the bilayer bulk of the aggregates. However, 20-43% of the DHPC takes part in the bilayer, corresponding to 6-12% of the bilayer being made up of DHPC. This fraction increases with increasing temperature. At temperatures above 45 degrees C, the aligning phase collapses.