Different glucocorticoid preparations modify the immune reaction in different ways. In this paper, the therapeutic efficacy of two glucocorticoids, deflazacort (DFZ) and prednisone (PDN), are discussed in relation to a group of 30 patients with systemic lupus erythematosus (n = 12) or rheumatoid arthritis (n = 18). The disease sub-groups were divided into two arms, one of which was treated with DFZ and one with PDN in a double-blind protocol. The results of this study indicate that DFZ and PDN induced a clinical remission within 1 month which was maintained until the 6th month. Nevertheless, certain immunological modifications, including a significant reduction of the circulating T lymphocyte level and of the CD4/CD8 ratio, which was between 1 and 1,5 during the DFC treatment and between 1 and 2 during the PDN treatment, are more pronounced and more stable with DFZ than with PDN. Moreover, DFZ has a smaller effect on calcium and glucose metabolism than PDN since the serum glucose and calcium level of patients treated with PDN increased respectively from 90 up to 130 mg/dl and from 9,5 to 11,5 mg/dl whereas those of patients treated with DFC remained within the normal range. These findings indicate that DFZ may have advantages over PDN in the treatment of immune-mediated diseases.