A molecular mechanism of somaclonal variation is proposed Oxidative stress caused by altered oxygen regime, the disturbance of the normal antioxidant status and the presence of strong prooxidants in cell culturing media are suggested to be the main reasons of the variations. Primary, secondary and final products of lipid peroxidation caused by oxidative stress can be directly responsible for plant genome instability. The proposed mechanism of somaclonal variation could be the basis for development of new biotechnological approaches to this process.