Vacuoles were prepared from endosperm tissue of 4-day-old castor bean seedlings (Ricinus communis var. Hale) and purified on a stepped sucrose gradient. It was shown by assays of marker enzymes that there was only trace contamination of the final preparation by other organelles (mitochondria, glyoxysomes, nuclei, spherosomes, and plastids) and by cytoplasmic components. Hydrolytic enzymes (acid protease, carboxypeptidase, phosphodiesterase, RNAase, phytase and beta-glucosidase) were present in the isolated vacuoles in amounts indicating a primarily vacuolar localization in vivo. The vacuoles also contained storage protein and high concentrations of sucrose. The over-all results indicate that the vacuoles from castor bean endosperm are the site of hydrolysis of the constituents of the protein bodies and are a temporary storage compartment for the sucrose produced from fat and protein reserves.