Various aspects of cyclic AMP and cyclic GMP metabolism are being investigated in bovine and human corneal epithelium, stroma and endothelium. These include characterizations of adenylate and guanylate cyclases, cyclic AMP and cyclic GMP-dependent protein kinases and cyclic nucleotide phosphodiesterases in the corneal layers. Corneal cyclic AMP responses to various stimuli is being studied and these responses correlated with protein kinase activation. Particular emphasis is placed on identification of protein kinase substrates and their enzymatic alteration which lead to the physiological responses in the cornea.