Established with the personal participation of O.G. Gazenko, the Russian system of medical care for cosmonauts' health has been largely preserved till this day. The system was fully functional on board the orbital complex MIR and, with appropriate modifications, has been adopted as a core of the medical care for Russian members of the ISS crews. In the period of 2000-2008, 22 cosmonauts were members of 17 ISS increments from 140 to 216 days in duration. The main functions of the medical care system were to control health, physical and mental performance, and to support implementation of space researches. The flow of readaptation to the normal gravity was, in most cases similar to what has been typical on return from the Russian orbital stations; some deviations are accounted for by application of the in-flight countermeasures. The paper familiarizes reader with some aspects of the theoretical work of academician O.G. Gazenko in the field of medical care in space flight. It outlines the principles of ISS medical management. The integrated medical support system combines medical equipment and items available on the Russian and US segments; the integrated medical group consists of flight surgeons, medical experts and biomedical engineers of the international partners and coordinates planning and implementation of medical operations. Also, challenges of health care on the phase of ISS utilization are defined.