cGMP signaling regulates epithelial fluid transport by Drosophila Malpighian (renal) tubules. In order to directly evaluate the importance of cGMP-degrading phosphodiesterases (PDEs) in epithelial transport, bovine PDE5 (a bona fide cGMP-PDE), was ectopically expressed in vivo. Transgenic UAS-PDE5 Drosophila were generated, and PDE5 expression was driven in specified tubule cells in vivo by cell-specific GAL4 drivers. Targeted expression was verified by PCR and Western blotting. Immunolocalization of PDE5 in tubule confirmed specificity of expression and demonstrated localization to the apical plasma membrane. GAL4/UAS-PDE5 tubules exhibit increased cG-PDE activity and reduced basal cGMP levels compared with control lines. We show that wild-type and control tubules are sensitive to the PDE5-specific inhibitor sildenafil and that GAL4/UAS-PDE5 tubules display enhanced sensitivity to sildenafil, compared with controls. cGMP content in GAL4/UAS-PDE5 tubules is restored to control levels by treatment with sildenafil. Thus bovine PDE5 retains cGMP-degrading activity and inhibitor sensitivity when expressed in Drosophila. Expression of PDE5 in tubule principal cells results in an epithelial phenotype, reducing rates of basal and cGMP-/Cardioaccelatory peptide(2b)(CAP(2b))-stimulated fluid transport. Furthermore, inhibition of PDE5 activity by sildenafil restores basal and cGMP-stimulated fluid transport rates to control levels. However, corticotrophin releasing factor-like-stimulated transport, which is activated by cAMP signaling, was unaffected, confirming that only cGMP-stimulated signaling events in tubule are compromised by overexpression of PDE5. Successful ectopic expression of a vertebrate cG-PDE in Drosophila has shown that cG-PDE has a critical role in tubule function in vivo and that cG-PDE function is conserved across evolution. The transgene also provides a generic tool for the analysis of cGMP signaling in Drosophila.