||The aim of the study was to evaluate methods applicable in a clinical setting for monitoring of changes in lung function in awake young children. Impedance measurements by the impulse oscillation technique (ZIOS), respiratory resistance measurements by the interrupter technique (Rint) and transcutaneous measurements of oxygen tension (Ptc,O2) were compared with concomitant measurements of specific airway resistance (sRaw) and forced expiratory volume in one second (FEV1) by whole body plethysmography and spirometry, respectively, during methacholine challenge in 21 young children aged 4-6 yrs, with suspected asthma. Measurements with each technique were repeated after each challenge step. A special face-mask was developed with an integrated mouthpiece which ensured mouth breathing during the measurements. The order of sensitivity of the techniques to assess methacholine-induced changes in lung function was ZIOS > sRaw > Ptc,O2 > FEV1 > Rint. ZIOS was significantly more sensitive than all subsequent methods, and Ptc,O2 was significantly more sensitive than FEV1. ZIOS, sRaw and Rint, but not Ptc,O2 and FEV1, detected the subclinical increase in bronchial muscle tone in the children during baseline, which was revealed by the significantly reduced airway obstruction after inhalation of a beta 2-agonist as compared to baseline. It is concluded that ZIOS, Rint and Ptc,O2 change in parallel with sRaw and FEV1 and with a comparable sensitivity during simultanoeous measurements of the response to methacholine in young children aged 4-6 yrs. This implies that ZIOS, Rint and Ptc,O2 provide convenient indices of changes in lung function. Their combined use will be useful for monitoring airway diseases of young children.