Background. Population aging is a global phenomenon with significant and diverse impacts on society. The average life expectancy of the population of Russia, especially men, lags behind economically developed countries. One of the priorities of the policy of our state is to improve the demographic situation and, first of all, to reduce the mortality of the population from manageable causes. Aim: to determine correlations between indicators of biological aging and the studied parameters of daily cortisol secretion. Materials and methods: 91 middle-aged men (45-59 years) were examined, the average calendar age was 51.61 ± 0.57 years. Biological age was determined automatically using a VaSera VS-1500 sphygmomanometer (Fukuda Denshi, Japan) according to the standard method. Blood cortisol concentration was determined twice with an interval of 12 hours. The features of circadian rhythms of cortisol secretion were determined. Statistical processing of the study results was carried out on a personal computer using the SPSS 21 software package. The critical significance level for all types of statistical analysis was taken equal to 0.05. Results. The rate of aging and circadian rhythms of secretion of the stress hormone, cortisol, among men of working age were analyzed. In order to search for new biological markers of aging, a correlation between the indicators of biological aging and the studied parameters of daily cortisol secretion was determined in the work. When analyzing the morning secretion of serum cortisol in patients of all studied groups, significant differences were revealed compared with group I (p