[Statistical approach to the validity of a diurnal cycle with periods of 4-6 hours]

Confidence coefficient and reliability of previously unknown phenomenon of the interdian cyclicity (with the periods about 4-6 hs) in dynamics of physiological and pathological processes is shown. Discovery of critical time instances (at 2, 9, 14, 18, 22 o'clock of local "winter" decree time) of human life poses a problem of an application of this phenomenon to the solution of different medical and social problems.