Methods are described for isolating adult rabbit retinal and maintaining it in a medium designed to resemble CSF. Morphologic, metabolic, nd electrophysiologic measurements obtained on the in vitro retinas showed that they remained in a nearly physiological state for at least 8 h, and even after 2 days in vitro they still exhibited a high level of metabolic activity and electrical responsiveness to light. Physiological activity was modified by photic stimulation, and data are presented to document changes in metabolism in response to the changes in function. The isolated retina appears to offer a number of unusual advantages for studying relationships between function and metabolism in organized mammalian central nervous tissue.