Objectives: To explore associations between LCI and FEV 1 , and IL8 and IL-1β in BAL fluid in closely monitored CF children at steady state conditions and during episode with increased LCI.Influence from BAL culture results on IL-8 and IL-1β was investigated.Methods: Prospective randomized study in 30 CF children.MBW, spirometry and BAL were performed at inclusion and every 3 month, the latter however only in half of the cohort when a predefined increase in LCI of >1 unit above baseline value occurred.BAL fluid from both lungs was analyzed for IL-8 and IL-1β and cultured.Results: Mean age: 10.6 (6.4-16.7)years, baseline LCI: 9.2 (6.2-13.5)and FEV 1 z-score was -0.02 (-2.04-1.32).Since IL8 and IL-1β on right and left side were highly correlated (r = 0.9 p < 0.0001) and (r = 0.6 p < 0.0019) mean values were used.LCI showed significant correlation with IL-1β (r = 0.45 p = 0.03) whereas no correlation was shown with IL8 levels (r = 0.07 p = 0.75).No correlations between FEV 1 z-score and cytokines were found.In patients randomized to additional BAL during first measurement of elevated LCI compared to baseline (mean increase: 2.4 units) there was no significant elevation of IL8 or IL-1β and no significant difference according to positive BAL cultures.Conclusions: In this study with a limited number of children with stable and mild CF, we found that LCI correlated significantly with level of IL-1β, but not with levels of IL8, and surprisingly, neither IL8 or IL-1β increased significantly at times of LCI elevation, nor were they significantly higher in culture positive BAL fluids.