[Biorhythm status as 1 of the selection criteria for cosmonauts]

The concept of biorhythmological status of the human body understands it as a sum total of biorhythmological characteristics of the organism. The status is discussed in two aspects: constancy and variability of circadian rhythns of vital functions. The relationship between the two parameters is described in the light of a hierarchic structure of the circadian system. The dependence of stress-resistance upon integrity and level of organization of the circadian system is ascertained. The importance of assessment of biorhythmological status for proper cosmonaut selection is emphasized.