Raman spectra of aqueous solutions of DPPC-cholesterol mixtures with 0, 10, 20, 30, and 30 mol % cholesterol are recorded at room temperature and at 60 degrees C within the pressure range from 1 bar to 30 kbar. In addition, at normal pressure a detailed temperature study is performed between 20 and 60 degrees C. Spectral parameters, such as frequencies, intensities, band shapes, and band splittings are analyzed to provide information on conformer population, reorientational fluctuations, acyl chain interactions, and phase transformation of the DPPC-cholesterol mixtures. Evidence for the formation of the new phase, orthorhombic GV phase, is provided and discussed. The correlation field splitting of the CH2 bending mode is used to discuss the structure, degree of disorder, and relative orientation of acyl chains in various phases and in the presence of cholesterol. Cholesterol induces reorientational disorder in the lipid molecules. Increased cholesterol concentration results in phase transformations being observed over progressively broader pressure ranges. Cholesterol makes the lipid membrane less sensitive to the external parameters such as hydrostatic pressure. The different pressure behavior of Raman and IR bands is explained in terms of the change in volume associated with Raman and IR active modes.