The intact chromaffin granule has been studied by high resolution proton and phosphorus magnetic resonance spectroscopy. In the granule the proton peaks of adrenaline and ATP are shifted upfield differentially with respect to their positions in free solution. All lines in both proton and phosphorus magnetic resonance spectra were considerably broadened. The n.m.r. spectrum of the chromogranin protein in the vesicles was also well resolved. A structure of the vesicle is proposed.