In the article is presented five-year experience of experimentation in autonomic regulation of blood circulation onboard the International space station. The heart rate variability (HRV) analysis was the basic methodical approach in the researches. We described probabilistic approach created on the basis of HRV analysis to an estimation of risk of pathology development in the conditions of long space flight. The individual type of autonomic regulation had essential value during the analysis of results. It is shown that the type of regulation, which is inherent in every cosmonaut in the conditions of weightlessness, remains even during following flights. We obtained the new scientific data on connection of character of adaptable reaction of an organism to the space flight factors with individual type of autonomic regulation. It is shown that staying in weightlessness is connected with changeover of regulatory systems and with transition in a zone of prenosological states. Adaptable reactions in weightlessness are characterized by tension growth of regulatory systems at preservation of sufficient functional reserves. The mobilization of additional resources after returning to the Earth is required and consequently functional reserve of mechanisms of regulation decreases. Cosmonauts with vagotonic and normo-sympatotonic types of autonomic regulation appear to be the most resistant. Knowing the type of autonomic regulation we will be able to foresee possible reaction of the cosmonaut to the factors of space flight. As a result of HRV analysis during the flight of the past few months likelihood estimations were calculated and risk categories were defined. Consequently, 3 groups of risk of pathology development were distinguished. In conclusion, theoretical and applied relevance of the conducted experiments were considered.