  We have identified two new galaxies with gas counter-rotation (NGC1596 and
NGC3203) and have confirmed similar behaviour in another one (NGC128), this
using results from separate studies of the ionized-gas and stellar kinematics
of a well-defined sample of 30 edge-on disc galaxies. Gas counter-rotators thus
represent 10+/-5% of our sample, but the fraction climbs to 21+/-11% when only
lenticular (S0) galaxies are considered and to 27+/-13% for S0s with detected
ionized-gas only. Those fractions are consistent with but slightly higher than
previous studies. A compilation from well-defined studies of S0s in the
literature yields fractions of 15+/-4% and 23+/-5%, respectively. Although
mainly based on circumstantial evidence, we argue that the counter-rotating gas
originates primarily from minor mergers and tidally-induced transfer of
material from nearby objects. Assuming isotropic accretion, twice those
fractions of objects must have undergone similar processes, underlining the
importance of (minor) accretion for galaxy evolution. Applications of gas
counter-rotators to barred galaxy dynamics are also discussed.
