Ion transport and the electric profile of distal airways of sheep lungs were studied in a miniature polypropylene chamber with a 1-mm aperture. Small airways with an inner diameter < 1 mm were isolated, opened longitudinally, and then mounted as a flat sheet onto the 1-mm aperture where it was glued and secured with an O-ring. Both sides of the tissue were bathed with identical physiological solutions at 37°C and oxygenated. Pooled data from 27 distal airways showed an inner airway diameter of 854 ± 22 (SE) µm and a transepithelial potential difference (PD) of 1.86 ± 0.29 mV, lumen negative. Short-circuit current (I_sc) was 25 ± 3.5 µA/cm², tissue resistance was 96 ± 14 , and conductance was 15.2 ± 1.7 mS/cm². At baseline, amiloride-sensitive Na transport accounted for 51% of I_sc (change in I_sc = 9.7 ± 2.6 µA/cm²; n = 8 airways), corresponding to 0.36 µeq · cm² · h¹. Treatment with 0.1 mM bumetanide did not reduce the I_sc (n = 5 airways). Exposure to 1 µM Ca ionophore A-23187 raised the I_sc by 9 µA/cm² (47%; P < 0.03; n = 6 airways). The latter effect was blunted by bumetanide. Carbachol at 1 µM provoked a biphasic response, an initial rapid rise in I_sc followed by a decline (n = 3 airways). There was no significant increase in PD or I_sc in response to isoproterenol or dibutyryl cAMP. The data suggest that Na absorption constitutes at least 50% of baseline transport activity. Cl or other anion secretion such as HCO₃ appears to be present and could be stimulated by raising intracellular Ca.