We investigated the effects of 17-estradiol and progesterone on transepithelial electrical resistance (R_TE) in sheep visceral and parietal pleurae. Specimens of intact pleurae from adult female sheep were used. The samples were transferred to the laboratory within 30 min after death of the animal in a Krebs-Ringer solution at 4°C. The pleura was then mounted as a planar sheet in Ussing-type chambers, and electrical measurements were made. There was an increase in R_TE in all of the samples examined after addition of 17-estradiol and progesterone in visceral and parietal pleurae. This increase was rapid within 1 min, lasted for ~15 min, returned to the basal level within 30-45 min, and was dose dependent. Tamoxifen, an estrogen receptor antagonist, did not significantly eliminate the effect of 17-estradiol. Furthermore, no steroid receptors were identified in cytosolic preparations of visceral and parietal pleura with ligand binding assays. The estrogen- and progesterone-induced increase in R_TE in both visceral and parietal pleurae was affected by addition of an inhibitor of nitric oxide synthase. Indeed, previous administration of N-nitro-L-arginine methyl ester prevented the increase in R_TE by 17-estradiol and progesterone. These results suggest that 17-estradiol and progesterone induce an increase in R_TE in both visceral and parietal pleura and thus alter the transepithelial permeability. The effect of steroids may be accounted for by rapid release of nitric oxide in pleura.