The effect of long term inhalation of hypertonic saline in subjects with cystic fibrosis on lung function, incidence of respiratory tract infections, quality of life, quantitative microbiology and sputum cytokine profile. The hypothesis is that regular inhalation of nebulised hypertonic saline will have a beneficial effect on lung function and other clinical outcomes with no adverse effects on infection and inflammation in adults and children with cystic fibrosis.