Experiments were designed to determine whether the enterotoxins of Vibrio cholerae, Escherichia coli, and Shigella dysenteriae type 1 alter the movement of fluid and electrolytes in the rat cecum. Net secretion of water and sodium were observed after incubation of 1.67 X10(-5) mug of purified cholera toxin (choleragen)/ml for 18 hr or of 50 mug/ml for 3 hr. The effect of choleragen on cecal transport of water and electrolytes was related to the dose. In addition, choleragen increased cecal mucosal content of adenosine 3':5'-cyclic phosphate but did not alter the histology of the cecum. The results demonstrate that the colon responds to choleragen in a manner similar to that of other tissues. In contrast, the enterotoxins of both E. coli and S. dysenteriae type 1 failed to affect cecal transport of water and electrolytes. These observations may explain several phenomena associated with the diarrhea produced by bacterial enterotoxins.