Characteristics of the subtransition in distearoyl phosphatidylcholine multilamellar dispersion were investigated by differential thermal analyses and x-ray diffraction under high pressure. Two phase transitions other than the well-know pre- and main-transitions were seen when the phospholipid was pressed above about 250 MPa and then once heated beyond the melting temperature. These phase transitions were accompanied by distinct changes of the chain-packing conformation from an orthorhombic symmetry to a quasihexagonal one. It is hypothesized that the subtransition under atmospheric pressure splits into these two transitions as a result of high-pressure melting.