The short-circuit current technique was used to examine the effects of N²-L-lysylbradykinin (LBK) on chloride secretion in the mucosae of the mouse intestine. It was found to be a potent chloride secretagogue in the mucosa lining the colon, jejunum, and cecum, as it is in most mammals, with 2 nM being sufficient to cause half-maximal secretion. The extent of the responses was in the order cecum > colon > jejunum. In cystic fibrosis (CF) null mice, with no CF transmembrane conductance regulator (CFTR) chloride channels, LBK caused no chloride secretion, but transporting activities for other ions were revealed. Introduction of the human CF gene into the genome of CF null mice at the zygote stage restored the chloride secretory activity of LBK, with only minor differences in potency. In mice in which the kinin B₂ receptor gene had been disrupted, LBK had no effect, whereas the responses to forskolin were unchanged. Thus the acute effects of kinins on chloride secretion depend uniquely on kinin B₂ receptors and CFTR chloride channels, which form the primary and final effector mechanisms of the secretory process.