Glucocorticoids are anti-inflammatory and immunosuppressive agents with pleiotropic effects on the growth, differentiation, and functional activity of T lymphocytes. The comprehensive assessment of the influence of dexamethasone on the functional activity of T cells with different grades of differentiation was performed under experimental in vitro conditions. We established that dexamethasone suppressed the functional activity of CD45RA⁺ and CD45RO⁺ T lymphocytes. In the population of naive (CD45RA+) T cells, the inhibitory effect of dexamethasone on the early activation stages (IL-2-dependent, associated with the CD25 expression and IL-2 production) was more significant, whereas in the culture of primed memory cells (CD45RO⁺), dexamethasone affects the later stages (IL-2-independent, associated with the expression of proliferation molecule CD71). Multidirectional effects of dexamethasone on the level of expression of mRNA of telomerase catalytic unit (hTERT) were associated with the degree of T cells differentiation. Most likely, the role of glucocorticoid hormones in immunogenesis is mainly the suppression of the excessive growth of T cells and the maintenance of the clonal balance in lymphoid tissue.