The mean electromotive force is considered in a differentially rotating flu
id taking into account stretching of the turbulent magnetic field. Calculat
ions are performed by making use of the second order correlation approximat
ion. Nonuniformity of the angular velocity leads to specific drift processe
s in the azimuthal direction. Due to this drift the magnetic field can rota
te with a somewhat different angular velocity than the fluid. Differential
rotation can also lead in a new instability of a non-axisymmetric mean held
. Regardless of the law of the differential rotation this instability can r
esult in an exponential amplification of the field.