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We used high-resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) to identify hormonally regulated proteins in cultured human fetal lung. Proteins labeled with [35S]methionine were separated by 2-D PAGE, and fluorograms were analyzed by computer-assisted analysis of densitometric scans. Dexamethasone (10 nM) and gamma-interferon (10 ng/ml) induced (2- to 22-fold vs. control) distinct sets of proteins (comprising approximately 2% of approximately 1,000 resolved proteins). Treatment with forskolin (10 microM) plus 3-isobutyl-1-methylxanthine (IBMX, 100 microM), which increases intracellular adenosine 3',53'-cyclic monophosphate (cAMP), induced both unique proteins and several proteins induced by dexamethasone. One protein (Mr 40,000, pI 4.4) was induced only with combined dexamethasone and cAMP treatment. Dexamethasone repressed four proteins, but inhibition was not observed with other hormones. Some of the regulated proteins were enriched in either fibroblasts or type II cells isolated from lung explants. We found no proteins that were consistently regulated by triiodothyronine (T3) (2 nM) or transforming growth factor-beta (10 ng/ml). Additionally, none of the hormonal treatments substantially altered the rate of methionine incorporation into total protein. Thus we have identified separate subsets of proteins that are regulated by glucocorticoids, gamma-interferon, and cAMP; these proteins may be important mediators of hormonal effects in the developing fetal lung.