In order to reduce the need for invasive diagnostic tests in pediatrics, there has been a rapid development of tests based on the analysis of exhaled air for the investigation of a wide range of conditions. These tests are frequently extensions of procedures that have been developed and more intensively investigated for use in adults. Consequently, when these tests are used for children, the procedures are modified and diagnostic cutoff values are changed, and this results in lack of standardization and the possibility of differences of clinical interpretation. (C) 2008 Elsevier B.V. All rights reserved.