To date, the only evaluations of the safety of HS in infants with CF have been small single-dose studies. There has been no evaluation of the tolerability of chronic HS administration. The goal of this study is to assess the safety and tolerability of exposure to 14 days of 7% HS administered twice daily in infants with CF, prior to enrolling subjects in the planned large, randomized, controlled trial. Conduct of this study will provide evidence for the tolerability of chronic HS administration in infants with CF and estimates of the proportion of infants who do not tolerate chronic HS treatment. The results will be used to establish the appropriate measures of tolerability at enrollment in the ISIS trial, and to refine sample size estimates to account for withdrawal due to intolerance of HS.