In cystic fibrosis (CF), airway inflammation causes an increased production of reactive oxygen species, responsible for degradation of cell membranes. During this process, volatile organic compounds (VOCs) are formed. Measurement of VOCs in exhaled breath of CF patients may be useful for the assessment of airway inflammation. This study investigates whether "metabolomics' of VOCs could discriminate between CF and controls, and between CF patients with and without Pseudomonas colonization. One hundred five children (48 with CF, 57 controls) were included in this study. After exhaled breath collection, samples were transferred onto tubes containing active carbon to adsorb and stabilize VOCs. Samples were analyzed by gas chromatography-time of flight-mass spectrometry to assess VOC profiles. Analysis showed that 1099 VOCs had a prevalence of at least 7%. By using 22 VOCs, a 100% correct identification of CF patients and controls was possible. With 10 VOCs, 92% of the subjects were correctly classified. The reproducibility of VOC measurements with a 1-h interval was very good (match factor 0.90 +/- 0.038). We conclude that metabolomics of VOCs in exhaled breath was possible in a reproducible way. This new technique was able to discriminate not only between CF patients and controls but also between CF patients with or without Pseudomonas colonization.