The temperature (T)-pressure (P) phase diagram of the ether-linked dihexadecylphosphatidylcholine (DHPC) multilamellar vesicles was constructed by the method of high-pressure optical density. The DHPC membrane at ambient pressure undergoes the pretransition (at 33.6 degrees C) from the interdigitated gel (L(beta)I) phase to the ripple gel (Pb) phase, and succeedingly the main transition (at 44.4 degrees C) from the P'(beta) phase to the liquid crystal (L alpha) phase. Since the slope of the T-P diagram for the pretransition, 0.316 K MPa(-1), is larger than that fbr the main transition, 0.242 K MPa(-1), the phase boundary between P'(beta), and L(beta)I phases disappeared at high pressure above 130 MPa. A triple point among L(beta)I, P'(beta) and L(alpha) phases was found at 130 MPa and 74.5 degrees C. Difference in phase diagrams between the ether-linked and ester-linked phospholipid bilayer membranes has been elucidated.