 Methods Children with CF n30 and children with asthma n40 were recruited included from our outpatient clinic. During this longitudinal study patients visit the outpatient clinic were followedup for 12 months; every two months during one year. patients visited our outpatient clinic. In addition to these standard visits, During exacerbations patients four extra visits were planned during an exacerbation. were asked to visit the University Hospital Maastricht four times. These additional visits were planned with a maximum of two times during the study. By means of a home monitor, children were asked to assess measurements of Besides measurements in the University Hospital, children measured forced expiratory volume in one second FEV1 at home using a home monitor, to record medication use, and, to record presence and severity of pulmonary symptoms. Outcome parameters were: 1 FeNO assessment in exhaled air, 2 inflammatory markers in EBC, 3 lung function parameters, 4 specific questionnaires to assess asthma and CF control and severity, 5 data originating from the home monitor. 