This was the first study of age-related differences of the cardiovascular system functioning and reactions to the LBNP test in career cosmonauts. Results of 174 LBNP tests performed within the standard medical monitoring program using Gamma-01 (orbital station Mir) and Gamma-lM (ISS) were subjected to comparative analysis. Thirty eight cosmonauts–members of 25 long-duration Mir and ISS missions were divided into two age groups, i.e. 30-39 y.o. (mean 36 & 0.7, 39% of all subjects) and 40-55 y.o. (mean 46 & 0.8, 61% of all subjects). The testing was performed before launch and in flight (typically on FD-120). Age-specifc changes in the hemodynamic status were recorded in resting cosmonauts pre-flight and in spaceflight microgravity; relative dynamics of the CV parameters in response to standing posture imitation was on one and the same patterns and yet demonstrated unequal intensity before and in flight. Test results implicate that analysis and interpretation of cosmonauts' medical monitoring data should take into account individual age, which is of particular practical importance when dealing with the LBNP test data obtained in different periods of space flight.