the transport of na/sup +/ and cl/sup -/ across trachea excised from fetal dogs was evaluated from transepithelial electrical properties and isotope fluxes. under basal conditions the tissues were characterized by a lumen-negative potential difference (pd) of 11 mv and conductance of 5.2 ms/cm/sup 2/. the short-circuit current (i/sub sc/) was 43 mu a/cm/sup 2/ (1.6 mu eq.cm/sup -2/.h/sup -1/). basal na/sup +/ flows were symmetrical, but net na/sup +/ absorption (1.1 mu eq.cm/sup -2/.h/sup -1/) could be induced by exposure of the luminal surface to amphotericin b (10/sup -6/ m). bilateral replacement of na/sup +/ reduced i/sub sc/ by 85 percent . replacement of submucosal na/sup +/ or exposure to submucosal furosemide (10/sup -4/ m) reduced net cl/sup -/ secretion by 60-70 percent . luminal exposure to indomethacin (10/sup -6/ m) induced a 50 percent decrease in i/sub sc/, whereas isoproterenol (10/sup -6/ m) increased i/sub sc/ by 120 percent . the properties of the cl/sup -/ secretory pathway across fetal dog trachea are consistent with the model proposed for cl/sup -/ secretion across adult dog trachea and other cl/sup -/-secreting tissues (e.g bullfrog cornea and shark rectal gland). the absence of basal na/sup +/ absorption by fetal dog trachea probably reflects limited apical membrane na/sup +/ permeability