Diuresis mediated by the superior laryngeal nerve (SLN) was investigated using pentobarbital-anesthetized rats. A marked increase in urine flow was induced by application of water to the larynx. The diuretic effect of water was conspicuous during the first 30 min after the application and lasted for more than 1 hr. In contrast, a 160 mM solution of NaCl produced only slight diuresis. After bilateral sectioning of the SLNs, water-induced diuresis was considerably reduced. The results suggest that water fibers contained in the SLN may make a major contribution to the diuresis.