Аннотация:We study the so-called "no-z" approximation to the mean field dynamo equations, as applicable to spiral galaxies. We investigate the circumstances in which sharp magnetic field structures (fronts) can appear and propagate radially, and derive an expression for the speed of propagation. Two kinds of fronts are discussed. The exterior front is a transition layer between a region in which magnetic field is absent and in which the value of the field differs essentially from zero. The interior front is a transition layer between two regions which differ in the direction of the field present. The speed of an interior front is shown to be proportional to η/Rg (where η is diffusivity and Rg is the galactic radius), whereas the exterior front moves with speed of order √{γη}, where γ is the local growth rate of the dynamo.