Most amino acids are, like glucose, co-transported with sodium and are thereby potential additives to oral rehydration solutions for the treatment of diarrhea. In this study the effects of mucosal amino acids on short-circuit current and Na and Cl fluxes in three segments of the porcine small intestine were studied. L-alanine, L-leucine, L-lysine, L-proline, L-phenylalanine and L-glutamine were added (chamber concentration of each amino acid was 20 mmol x l-1) to the mucosal side of stripped proximal, mid, and distal small intestine sheets mounted in Ussing chambers in glucose containing (16 mmol x l-1) bathing medium; electrical parameters and unidirectional fluxes were measured. The amino acids induced a significant elevation in mucosa to serosa flux and unaltered serosa to mucosa flux of Na in all three segments, resulting in significant elevation in net Na absorption in proximal (2.4 +/- 0.3 microEq x cm-2 x hr-1 to 3.5 +/- 0.3 microEq x cm-2 x hr-1, P < 0.05), mid (5.9 +/- 0.5 microEq x cm-2 x hr-1 to 8.1 +/- 0.7 microEq x cm-2 x hr-1, P < 0.05) and distal (5.9 +/- 0.6 microEq x cm-2 x hr-1 to 8.3 +/- 0.7 microEq x cm-2 x hr-1, P < 0.05) small intestine. The mucosa to serosa Cl flux was significantly elevated in all three segments (P < 0.01) by amino acids abolishing the net Cl secretion in proximal (2.5 +/- 0.4 microEq x cm-2 x hr-1 to 0.8 +/- 0.6 microEq x cm-2 x hr-1, P < 0.01) and mid (2.2 +/- 0.4 microEq x cm-2 x hr-1 to 0.1 +/- 0.9 microEq x cm-2 x hr-1, P < 0.01) small intestine. The changes in SCC were carried by the electrogen Na absorption. In conclusion, the amino acids, in addition to glucose, stimulate Na absorption by about 1.0 microEq x cm-2 x hr-1 in the proximal part, and 2.5 microEq x cm-2 x hr-1 in the mid and distal part of the small intestine.