  We analyze the magnetic-field profiles H_z(x) at the upper (lower) surface of
a superconducting strip in an external magnetic field, with z perpendicular to
the plane of the strip and x along its width. The external magnetic field H_a
is perpendicular or inclined to the plane of the strip. We show that an
asymmetry of the profiles H_z(x) appears in an oblique magnetic field H_a and
also in the case when the angular dependence of the critical current density
j_c in the superconductor is not symmetric relative to the z axis. The
asymmetry of the profiles is related to the difference \Delta H_z(x) of the
magnetic fields at the upper and lower surfaces of the strip, which we
calculate. Measurement of this difference or, equivalently, of the asymmetry of
the profiles can be used as a new tool for investigation of flux-line pinning
in superconductors.
