The kinetics of the structural phase transitions of dipalmitoylphosphatidylcholine (DPPC) in excess water have been investigated by simultaneous small- and wide-angle detection in millisecond time-resolved synchrotron x-ray diffraction. The transition from the rippled to liquidcrystalline phase (P′β(mst) - L a ) has been induced by an approx. 5°C temperature-jump within 2 ms using an erbium glass laser. The structural parameters, i.e., the long-range order of the bilayer stacking and the short-range order of the lateral lipid packing have been detected with 5 ms time-resolution. The experiments show that the intensities of both the small- and the wide-range reflections indicative of the P′β(mst)-structure decay in parallel and on the same time-scale as the first- and second- order reflections of the lamellar lattice of the L a -phase grow in intensity. For the ppretransition, we have made the important observation that the rearrangement of the hydrocarbon chains is slower than the initial changes in the long-range lamellar lattice.