The review summarizes the current data on synaptophysin (SYP), its functional role in the cell and the use of SYP immunocytochemistry for labeling the synaptic contacts. SYP is a transmembrane glycoprotein found in small presynaptic vesicles of the nerve cells and in microvesicles of the neuroendocrine cells. Literature data and the authors' own experience suggest that currently SYP is an important synaptic marker, which allows, with the use of light and confocal laser microscopy, to obtain the reliable data on the morphological organization of the synaptic structures in the central nervous system. It is also indispensable in the study of the efferent innervation of the internal organs. Applicatioin of the quantitative analysis of SYP-immunopositive structures using light and confocal laser microscopy allows to solve some problems that previously could be solved only by using electron microscopy.