Within the period of 2000 to 2012 the values of 40 diagnostically significant biochemical indices in venous blood were being determined during the pre-flight clinical and physiological examination of 28 Russian cosmonauts aged 35 to 54, members of main and back-up crews of expeditions to the International Space Station. The above examination was conducted 45-30 days prior to the launch. Taking account of the fact that each of the most of the cosmonauts performed several flights over the mentioned period and they were repeatedly included in back-up crews over and over again, each of cosmonauts participated in pre-flight examinations 1 to 5 times. Reference values were calculated for each of the studied indices. It was found that reference interval boundaries for 15 indices were narrower as compared to the generally accepted ranges. The upper boundaries of activity reference ranges of a number of enzymes, as well as of concentration of some metabolites of energy and plasticity metabolism were raised relative to mean population values. Thus, it was found that Russian cosmonauts being a specific professional team featured inherent reference values which differed from mean population values in a number of blood biochemical indices. It is conditioned by peculiarities of selection, physical training and psychic and emotional status of crew members during a pre-flight period.