  We present the ionized-gas kinematics and photometry of a sample of 4 spiral
galaxies which are characterized by a zero-velocity plateau along the major
axis and a velocity gradient along the minor axis, respectively. By combining
these new kinematical data with those available in the literature for the
ionized-gas component of the S0s and spirals listed in the Revised Shapley-Ames
Catalog of Bright Galaxies we realized that about 50% of unbarred galaxies show
a remarkable gas velocity gradient along the optical minor axis. This fraction
rises to about 60% if we include unbarred galaxies with an irregular velocity
profile along the minor axis. This phenomenon is observed all along the Hubble
sequence of disk galaxies, and it is particularly frequent in early-type
spirals. Since minor-axis velocity gradients are unexpected if the gas is
moving onto circular orbits in a disk coplanar to the stellar one, we conclude
that non-circular and off-plane gas motions are not rare in the inner regions
of disk galaxies.
