Activity of carbonic anhydrases (CA) especially that of the tumor-associated, transmembraneous CA IX, which is active at the outer cell surface, is required for cancer genesis and progression. Previous studies show that migrating melanoma (MV3) cells establish an extracellular proton gradient at their surface with the highest proton concentration at the leading edge of the lamellipodium and the lowest concentration at the rear end. Here, we investigate whether the CAs' contribution to cancer genesis and progression may be based on their possible function in cell migration. Cell migration was determined employing time lapse video microscopy. Unspecific inhibition of all CA isoforms by acetazolamide caused (i) the migratory speed of MV3 cells to decrease by ~33% and (ii) the cells to become more spherical by ~44% while cell adhesion remained unaffected. The strong expression of CA IX in MV3 cells was confirmed by Western blotting and immunolocalization indicates its association with components of the cytoskeleton. Specific inhibition of CA IX by 4(-2-aminoethyl)-benzenesulfonamide slowed cells down by ~15% and led to exactly the same morphological changes as acetazolamide. Again, cell adhesion remained unaffected. From these results we conclude that besides the membrane-bound CA IX the activity of which significantly affects cell migration other CA isoforms such as the cytosolic CA II must have effects on the migratory machinery.