Introduction: Achieving of good control in severe and refractory asthma requires long-term treatment with systemic glucocorticosteroid (GCS). The aim of this study was to determine, whether severe steroid dependent asthma associates with decreased sensitivity of peripheral blood lymphocytes to GCS, or altered expression of glucocorticoid receptor (GR) isoforms. The numbers of circulating Treg CD4/CD25high lymphocytes were also studied. Methods: The studied groups included: 25 patients with severe or refractory asthma, 15 with chronic moderate asthma, and 11 healthy subjects. Severe steroid dependent asthmatics (n=14) were selected within severe asthma group. We analyzed the influence of dexamethasone (DEX) on activation and proliferation of lymphocytes, as well as spontaneous and GCS induced apoptosis in vitro. The expression levels of α and β GR isoforms were studied using qPCR technique. Subpopulations of peripheral blood lymphocytes were counted by flow cytometry. Results: Expression of GR isoforms was similar in all studied groups, and high GRα/GRβ ratio (approx. 250) indicates that contribution of β isoform in total GR pool is only marginal. In steroid dependent asthmatics there was no increased activation and proliferation of lymphocytes, nor decreased reactivity to DEX in vitro. In this group only partial inhibition of CD40L was observed (p<0.05). In steroid dependent asthmatics we found higher numbers of apoptotic lymphocytes in cultures with DEX. The percentage of CD4/CD25high was also increased in this group. Conclusions: The decreased sensitivity to GCS in severe and refractory asthma is not the consequence of impaired expression of GR isoforms, and does not result from abnormal T-cell reactivity. The elevated expression of CD40L may be the reason of the weaker reactivity to GCS observed in vivo. The induction of peripheral Treg CD4/CD25high pool in severe steroid dependent asthma is not disturbed and constitutes one of the most efficient mechanisms that is necessary to achieve good asthma control.