  The influence of electric felds and currents has been investigated in the
high-$T_c$ superconductors $YBaCuO$ and $BiSrCaCuO$ using a point-contact
geometry with $Ag$ as the counterelectrode, which reveal switching transitions
between states of a different resistance. The origin of this effect in point
contacts is associated with electromigration of the oxygen, driven by the
electric feld as well as by the currentinduced "electron wind". The switching
effect preserves its basic features at elevated temperatures up to room
temperature and in high magnetic felds up to 10 T.
