The effects of a carbonic anhydrase inhibitor, acetazolamide, bound to a 72,000 dalton dextran (DBI) on bicarbonate and sodium fluxes across the isolated rabbit corneal endothelium have been examined. When DBI was present on the aqueous-facing endothelial surface, there was a marked inhibition of both the stromal to endothelial unidirectional and net flux of bicarbonate. This suggests that the exit of bicarbonate from the cell into the aqueous-facing solution is influenced by the enzyme carbonic anhydrase. No change was found in sodium fluxes under these same incubation conditions. When DBI was present on the stromal-facing surface of the endothelium, no changes were found in unidirectional or net bicarbonate fluxes; the sodium flux from stroma to endothelium was increased, however, with no change in net flux. This data implies that the link between sodium and bicarbonate movement across the endothelium is not a direct coupling between the transport of the two ions in the form of a symport (Na+:HC03−)t the apical cell border.