Cyclic AMP and cyclic GMP metabolism will be examined in preparations of lung. Cyclic nucleotide levels with and without various bronchodilating and bronchoconstricting agents will be examined in incubations of tracheal and bronchial smooth muscle, bronchial mucosa, alveolar macrophages, and peripheral pieces of lung. Guanylate cyclase will be purified and characterized from lung and its subcellular distribution examined. Cyclic GMP dependent protein kinase will also be studied and attempts made to define its naturally occurring endogenous substrates. BIBLIOGRAPHIC REFERENCES: Criss, W.E. and F. Murad: Urinary excretion of guanosine 3',5'-monophosphate and adenosine 3',5'-monophosphate in rats bearing transplantable liver and kidney tumors. Cancer Res. 36, 182-184, 1976. Criss, W.E., F. Murad and H. Kimura: Properties of guanylate cyclase from rat kidney cortex and transplant-able kidney tumors. J. Cyclic Nucleotide Res. 2, 11-19, 1976.