1. Four subjects with colonic exclusion for chronic hepatic encephalopathy were investigated by a perfusion technique in a study of water and electrolyte transport by the colon.
2. The mean values for water and electrolyte transport, mucosal potential difference and colonic volume compare closely with values previously obtained in the intact human colon.
3. A reduction in luminal pH did not affect water or sodium absorption, in contrast with previous animal studies, but did increase chloride absorption, probably on the basis of increased chloride-bicarbonate exchange.
4. Potassium secretion increased with a reduction in luminal pH, possibly as a result of the low pH increasing mucosal permeability.
5. It is concluded that the excluded colon in these patients provides a valid model for studies of normal colonic physiology.