my daughter was put on pulmozyme at 4 weeks and added xoepenex at 3 months...even though she didnt have any bacteria in her lungs, our doc explained that the inflammation and mucus buildup comes with cf from day one, even if they sound perfectly clear, etc... and the nebs should be used at first to help prevent alot of build up and inflammation. i know some docs dont like to use nebs until "noticable" problems arise, but i didnt like the sound of that. (but you will have alot of different opinions, as is the case with everything involving cf treatment!!!)