Freeze-etched preparations of rabbit neurohypophysis and isolated hormone granules from cow neurohypophyses were examined electron microscopically. Many features seen in conventionally prepared sections were also apparent in freeze-etched replicas, particularly the neurosecretory nerve-endings containing elementary granules and elongated pituicyte processes. Measurements of diameters of both isolated and hormone-containing granules in situ indicated that they were slightly larger in freeze-etched material than in that prepared by conventional electron microscopic techniques. Fractures through the cores of hormone-containing granules showed a lamellar internal structure of 4 nm periodicity in both species examined.