  We reconsider the problem of the formation of a large-scale magnetic field in
the accretion disks around black holes. In contrast with previous work we take
into account the nonuniform vertical structure of the disk. The high electrical
conductivity of the outer layers of the disk prevents the outward diffusion of
the magnetic field. This implies a stationary state with a strong magnetic
field in the inner parts of the accretion disk close to the black hole.
