Synaptophysin is a 38 kDa glycoprotein present in the membrane of neuronal presynaptic vesicles in brain, spinal cord, retina, vesicles of adrenal medulla, neuromuscular junctions, and endocrine cells. It is also expressed by neuroendocrine cells throughout the body, both normal and neoplastic. Synaptophysin is a useful marker for the identification of normal neuroendocrine cells and neuroendocrine neoplasms.