  The evolution of three-dimensional, large-scale, magnetic fields, in a
galactic disk is investigated numerically. The N-body simulations of galactic
dynamics are incorporated into the kinematic calculations of induction
equations to study the influence of non-axisymmetric gas flows on the galactic
magnetic field. The time-dependent gas velocity fields are introduced as input
parameters for the MHD-simulations. Our principal concern is to check how
dynamical evolution of the galactic gas affects the global magnetic field
structure and intensity. We have found that the magnetic field responds
sensitively to changes in the gas velocity field, and even slight variations of
the dynamical parameters, such as the gas mass/total mass ratio results in
nonuniform intensity structures, i.e. magnetic arms. The magnetic lines of
force are well aligned with spiral arms and bar due to compressional flows in
these features. In the inter-arm regions the areas with magnetic vectors going
opposite to the main magnetic spirals are present.
