Lyophilized purple membrane sheets have been investigated by C-13- and P-31-cross polarization/magic angle spinning NMR spectroscopy. The high-resolution C-13 spectrum and its non-quaternary suppression version indicate fast protein side-chain motions but a rigid backbone structure on a time scale of roughly less than 0.001 to 0.01 s. Three components of exchangeable hydrogen have been detected by deuterium NMR. The mean exchange time of the peptide hydrogens must be longer than 1 microsecond. The medium component is attributed to mobile side-chains. In addition a narrow line has been observed which is assigned to the residual hydration water.