Short chain fatty acids, particularly butyrate, stimulate electroneutral NaCl absorption from the colon. Their effect in colonic epithelia lacking basal electroneutral NaCl absorption is unknown. Butyrate is also reported to inhibit active Cl^- secretion in the colon. The present studies were undertaken to delineate the inter-relationships between the effects of butyrate on active Na⁺ and Cl^- transport in the colon. Studies were carried out in rabbit distal colon (known to have predominant electrogenic Na⁺ absorption), rat distal colon (characterised by electroneutral Na⁺ absorption), and hyperaldosteronaemic rat distal colon (characterised by electrogenic Na⁺ absorption). The effect of cholera toxin (CT) was also noted. Potential difference, short-circuit current (I_SC) and fluxes of Na⁺ and Cl^- were measured in stripped mucosa under voltage-clamp conditions. Butyrate stimulated electroneutral Na⁺ and Cl^- absorption in distal colon of normal and salt-depleted rats, and stimulated Na⁺ absorption in rabbit distal colon. Amiloride (10^-4 M) or CT did not inhibit this process. In rabbit distal colon, stimulation of Na⁺ absorption by butyrate was not dependent on the presence of Cl^- in the medium. Butyrate significantly decreased conductance, decreased flux of sodium from serosa to mucosa (particularly in rabbit distal colon), and decreased I_SC. Net Cl^- secretion, induced by CT, was completely inhibited by butyrate. Stimulation of Na⁺ absorption was independent of exposure to CT. Bumetanide reversed net Cl^- secretion to net absorption, but did not alter Na⁺ or Cl^- fluxes in tissues exposed to butyrate. Thus butyrate stimulates active Na⁺ absorption in colonic epithelia, with or without expression of basal Na⁺-H⁺ exchange. Independently, butyrate inhibits active Cl^- secretion induced by cAMP in these epithelia.