Sodium ion and chloride transport was studied in vitro in small intestinal and colonic tissue from patients with cystic fibrosis (CF) and from non‐CF control subjects matched as to age and sex. Normal histological appearance and substantial response to mucosal glucose (5 mM, ileum) or mucosal amiloride (10−5M, colon) indicated normal tissue viability in both control and CF tissues. Electroneutral NaCl absorption was demonstrated in the small intestine of control subjects and CF patients. Small intestinal and colonic tissues of control subjects responded to four secretagogues (theophylline, 5 mM; prostaglandin E2, 10−6M; calcium ionophore (A23187), 10−5M; bethanechol, 5 × 10−5M), with electrogenic chloride secretion. The tissues of CF patients, however, did not respond to any of the test secretagogues. These studies demonstrate that an abnormality in chloride transport is present in the small intestinal and colonic epithelia of CF patients. Unlike airway epithelia, which secrete chloride in response to Ca ionophore, the intestinal epithelia of CF patients do not respond to either cAMP‐ or Ca‐mediated secretagogues. This abnormality in intestinal electrolyte transport may play a role in the pathogenesis of meconium impactions in CF patients.— Berschneider, H. M.; Knowles, M. R.; Azizkhan, R. G.; Boucher, R. C.; Tobey, N. A.; Orlando, R. C.; Powell, D. W. Altered intestinal chloride transport in cystic fibrosis.FASEB J.2: 2625‐2629; 1988.