The exercise training has positive impact on autonomic nervous system (ANS) activity. However, specific type of these changes significantly depends on intensity of used physical exertion. THE AIM OF THE STUDY: To assess the influence of long-term and single moderate physical exertion on ANS function in young athletes. MATERIAL AND METHODS: Sixteen middle-aged, 19-34 years old (24 +/- 5) athletes were included in the study. Assessment of ANS parameters (baroreflex sensitivity--BRS-WBA, heart rate variability--HRV) and mean heart rate period (mean HP) were calculated three times: recording 1--during the final stage of training period, recording 2--60 minutes after single moderate exertion, recording 3--after 2 months of training before competitions. RESULTS: In the whole group, significant increase of TP, HF SDNN and rMSSD indices was found in recording 2 comparing to recording 1, whereas after 2 months of intensive training no statistically significant changes were observed. In the group of athletes training only endurance sport (12 persons) in recording 2 the significant increase of TP, HF, SDNN, rMSSD and BRS-WBA was found. After 2 months of intensive training, no changes of these parameters were observed. CONCLUSIONS: In response to long-term training cycle with increasing intensity, preparing athletes for competitions, no significant changes of measured ANS parameters were found, which may indicate lack of overtraining during such a high intensity of training, and its safety. The changes of ANS parameters indicating increase of parasympathetic nervous system function after single exertion with moderate intensity (65% of maximum heart rate) were observed.