The structural organization of respiratory enzymes oriented in a lipid bilayer matrix will be investigated by electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopy. The orientation of an enzyme in a lipid bilayer makes possible new types of spectroscopic studies, since the bilayers themselves can be aligned in parallel sheets of a multilamellar array. The EPR spectra of enzymes from bovine cardiac mitochondria show definite heme group orientation with respect to the bilayer plane, and the environment of other metal centers (e.g. Cu in cytochrome oxidase) may likewise be deduced from oriented-enzyme spectra. A method for obtaining high-resolution NMR spectra from membrane-bound metalloproteins will also be explored. Both these methods allow determination of the structure of enzyme complexes which are difficult to study by other means. The prospect of using the EPR method to characterize the multilamellar granules typical of certain muscle-cell respiratory defects will be discussed briefly.