To determine whether airway epithelium releases arginine vasopressin (AVP) and, if so, what the mechanism of the release is, we studied cultured human bronchial epithelial cell line, 16-HBE cells, in vitro. The cells spontaneously released small but significant amounts of AVP, and this release was dose dependently increased by platelet-activating factor (PAF) or bradykinin (BK). The PAF- and BK-induced AVP release was inhibited by 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate, a phospholipase C inhibitor, and thapsigargin but not by Ca2+ -free solution. Pretreatment with the big conductance Ca2+-activated K+ channel blocker iberiotoxin attenuated the stimulated release of AVP, whereas apamin and glibenclamide were without effect. These results suggest that human bronchial epithelial cells release AVP and that the release may be stimulated by phospholipase C activation, mobilization of Ca2+ from internal stores and the concomitant activation of big conductance Ca2+-activated K+ channels.