The main purpose of this research was to study the effects of water movement on arsenic absorption. In order to appreciate and measure the interaction between these two variables we investigated the perfusion of isotonic and hypotonic buffers (containing 3.2 microgram/ml As2 O5 into rat small intestines. The As (V) depended on osmolarity sensitive. This implied the presence of a saturable uptake kinetic mechanism and suggested the participation of some kind of carrier-mediated transport system. An increase in arsenate absorption and its accumulation in organs was detected in the presence of an Na+ gradient. The same technique, combining isotonic buffers with different pH values and buffers containing valinomycin, was used in order to study the effects of intraluminal pH on membrane potential. A significant decrease in arsenic levels and As(V) absorption in organs was detected as a result of an increase in the pH. This influence of pH on the As(V) absorption mechanism indicated dependence on a proton (H+) gradient. An inside negative potassium potential induced by valinomycin increased significantly the uptake of arsenate, suggesting an electrogenic transport of arsenate. In conclusion, the As(V) might be absorbed from the small intestine through a carrier-mediated mechanism, which would depend on the Na+(-) and H+(-)gradients and the membrane potential differential from both sides of the intestinal epithelial cells.