Age peculiarities of cardiorespiratory system reactions on isocapnic hypoxia (inhalation of gas mixture of 12% O2) have been investigated. It has been stated that breathing with hypoxic mixture resulted in more significant shift of O2 blood saturation, AP and autonomic balance in the elderly people (p < 0.05) comparing to the young people. It testifies to a greater intensity of sympathoadrenal system at hypoxic stress in elderly people that confirms the decrease of their tolerance to hypoxia.