The aim of the study was analysis of the spectral parameters of heart rate variability (HRV) in children and youth with different intensity of bronchial asthma. MATERIAL AND METHODS: The study was conducted in the group of 107 children and adolescents, aged 10-17 years, comprising 58 healthy subjects and 49 with bronchial asthma (22 with mild and 27 with moderate asthma). Spectral HRV parameters at rest and under active orthostatic test conditions (5 min--supine position, 5 min--standing position) were analysed in two age subgroups: group A--children aged 10-13 years and group B--youth aged 14-17 years. RESULTS: In both subgroups at rest a growing tendency for high frequency components (HF) of HRV spectra was observed together with greater intensity of asthma. In the youth group with moderate asthma, the HF component (40.8 +/- 14.0 n.u.) at rest was significantly higher (p < 0.05) than in the age-matched control (30.8 +/- 10.7 n.u.). In all the groups examined assuming erect position resulted in a significant rise in LF/HF index, which was most pronounced in the groups with mild (p < 0.01) and moderate asthma (p < 0.05). CONCLUSIONS: The study confirmed a significant association between the vagal activity in children and youth and frequency and intensity of bronchial asthma. A short-term HRV analysis can be utilised in the assessment of autonomic mechanism role in the development of bronchial asthma in children and youth.