We show that in a certain range of parameters the interaction between
vortices causes significant enhancement of galvanomagnetic effects in
thin superconducting films, as opposed to thick films. In particular,
the Nernst coefficient acquires a contribution exceeding the single-vo
rtex term at relatively small external magnetic fields. The possibilit
y of inducing the dc voltage due to either vortex-antivortex pair prod
uction by external ac currents or pair-breaking radiation is also disc
ussed. Our results give a possible explanation for the experiments of
A. Gerber and G. Deutcher.