The purpose of this study is to determine the safety and local tolerability of multiple dose administration of inhaled OligoG in CF subjects. Particular emphasis will be put on local, clinical tolerance, pulmonary function and pulmonary adverse events. The secondary purpose is to monitor the effect of multiple dose administration of inhaled OligoG on various efficacy variables, such as mucolytic activity, lung function, respiratory symptoms, Quality-of-Life and microbiological outcome measures.