Electrical stimulation of the occipital cortex resulted in discrete photic sensations or "phosphenes" in two volunteers who had been totally blind for 7 and 28 years, respectively. Stimulation of multiple electrodes allowed one patient to recognize simple patterns, including letters. Both patients made an uneventful recovery, and the success of these experiments reinforces the hope that a functional visual prosthesis can be developed, although many problems remain to be solved.