  The HI structure and kinematics of the peculiar starburst galaxy NGC 3310
(Arp 217, UGC 5786) are discussed. New evidence bearing on the origin of the
starburst is presented. The bulk of HI coincides with the bright optical disk
and shows differential rotation. Its velocity dispersion is, however, unusually
large for a spiral galaxy (up to 40 km/s), suggesting that the disk is highly
perturbed as already indicated by optical emission line spectroscopy. There
are, in addition, two prominent HI tails, one extending to the north-west and
the other, somewhat patchy, to the south. These HI tails, the perturbed
kinematics and the peculiar optical morphology strongly suggest a recent merger
between two gas-rich galaxies. This seems to have been a major merger in which
most of the gas in the inner parts has been preserved in neutral atomic form
and either one of the progenitor disks has survived or a new disk has formed.
