Spectral parameters (SP) of heart rate variability (HRV) and a duration of cardiointervals (RR) in 14 healthy male volunteers at the age of 23-36 years under the influence of acute normobaric hypoxia by respiratory gas oxygen-nitrogen mixture (9% O2, 25 min) were studied. The 300 cardiocycles at each of six experimental time points by ECG at II standart lead were registered. The parameters before hypoxia were (M +/- m): RR (s) 0.90 +/- 0.03; SP powers (ms2) TP 13 553 +/- 2789; VLF 3885 +/- 902; LF 4724 +/- 1062; HF 4945 +/- 1165. All parameters were about 21-25% less as compared to background in the 5th min of hypoxia. The decreasing was about 17% (RR) and 34-38% (SP) in the 10th min of hypoxia. At the 20th min of hypoxia all parameters but RR were increased to the background level. At last after hypoxia in the 5th min parameters RR were at the background level, SP were to 1.5-2 times higher. In the 15th min all parameters returned to initial levels.