Rho GTPases are molecules in the cells that line the airways that decrease the protein that makes nitric oxide (NOS). Rho proteins also increase inflammation in these cells. Rho proteins are increased in CF cells, and may partially explain the low NO and high inflammation seen in CF. Blocking the Rho protein in CF cells increases NOS, which can then produce more NO. The Rho protein can be inhibited with a drug, simvastatin (Zocor®). Simvastatin is used by millions of people to lower their cholesterol, is very safe, has few side-effects and is approved for use in children greater than 10 years of age. We propose that treating CF patients with simvastatin will increase NO produced (exhaled NO), and may decrease airway inflammation.