Tartu Children's Clinic has started to use impulse oscillation system (IOS) to assess lung function in children. To find out how reliable has been the use of a new method we aimed to describe the short-term repeatability of IOS measurement, changes after bronchodilator (BD) and to compare our results with published reference values. Children performed two sets of measurements (15 min apart) with a single IOS device (Jaeger, Germany). Results were reported as the mean of 3 measurements, repeatability for resistance at 5 Hz (R5) was described in the placebo group. BD response was expressed both in absolute and relative terms. Z scores for the baseline R5 values were calculated using published reference values. 117 children (aged 3 to 8 years) were studied (72 of them wheezers, 34 coughers and 11 healthy), 76 of them had the second measurement after salbutamol inhalation (300 mg). Median coefficient of variation for baseline R5 for the whole group was 6%. The mean absolute changes (SD) between two measurements for the placebo and BD group were 0.014 (0.111) and -0.135 (0.096) kPa/l/s, respectively. When changes after BD were expressed as % of the baseline, the mean (SD) change in R5 was -19.2 (12.5) %. The mean (95% CI) Z score for R5 was -1.08 (-1.31 - -0.85). In the present study, short-term repeatability of R5 was similar to that of previous studies. There was no difference between groups of children. Changes after BD were close to those from Malmberg et al. 2002 and Olaguibel et al. 2005. The interindividual scatter of R5 values was relatively large with our results being on average lower than the reference values from Malmberg et al. 2002. Malmberg, L.P. et al. 2002. Clin Physiol Func Im 22, 64–71. Olaguibel, J.M. et al. 2005. J Invest Allerg Clin Imm 15, 102–106.