  In this paper we present detailed theoretical analysis of the frequency
and/or magnetic field dependence of the surface impedance of a metal at the
anomalous skin effect. We calculate the surface impedance in the presence of a
magnetic field directed along the normal to the metal surface. The effects of
the Fermi-liquid interactions on the surface impedance are studied. It is shown
that the cyclotron resonance in a normal magnetic field may be revealed {\it
only and exclusively} in such metals whose Fermi surfaces include segments
where its Gaussian curvature turns zero. The results could be applied to
extract extra informations concerning local anomalies in the Fermi surface
curvature in conventional and quasi-two-dimensional metals.
