The dynamic behaviour of the probe molecules DPH and TMA-DPH embedded in small unilamellar vesicles and planar multibilayers of POPC has been studied by time-resolved fluorescence depolarization techniques. The molecular dynamics of the probe molecules was analysed in terms of the rotational diffusion model. It is found that analysis of the time-dependent fluorescence anisotropy from the vesicle system yields two distinct, though statistically equivalent solutions. On the other hand the measurements on planar multibilayers can be interpreted unequivocally. It is shown that the order parameters of the probe molecules are higher in the multibilayers than in the vesicles. A reconstruction of the orientational distribution function reveals that the TMA-DPH molecules have a more pronounced tendency to lie with their long axes parallel to the bilayer surface in the curved vesicles than in the planar multibilayers. An intriguing finding is that the reorientational motion of the probes is considerably slower in the multibilayer samples than in the vesicles. These differences are attributed to the curvature and higher hydration of the bilayers in the vesicle systems.