[Primary event in the process of membrane fusion]

Literature data on conditions required for membrane fusion were analysed. It has been shown that fusion proceeds only as a result of structural reconstructions of the bilayer. Classification of fusion mechanisms according to the primary event, including the structural change of the membrane, is suggested. Two main types of the primary events are singled out: the stalker one involving appearance of a bridge between the membranes drawn together, and the adhesion one involving structural reconstruction due to close adhesion of the membranes.