Stressful/inflammatory conditions activate the immune system and subsequently the hypothalamic-pituitary-adrenal (HPA) axis through the central and peripheral production of cytokines such as IL-6 and TNF-alpha. A relative adrenal hypofunction, as evidenced by inappropriately normal F levels and reduced DHEAS levels, has been recently claimed to play a causative role in the pathogenesis of autoimmune/inflammatory diseases such as rheumatoid arthritis (RA) and polymyalgia rheumatica (PMR). Thus, we evaluated baseline levels of adrenal androgens, IL-6 and IL-12 together with HPA axis challenge by ovine CRH and low-dose ACTH in premenopausal RA women and aged PMR women. In addition, adrenal steroids, IL-6, and acute-phase reactant levels were measured at baseline and during 12 months of glucocorticoid tapering regimen in a cohort of PMR patients. Reduced DHEAS levels (p<0.05) associated to increased (p<0.05) IL-6 and IL-12 levels were found in RA patients as compared to controls (C). Irrespective of the inflammatory condition, basal and stimulated cortisol levels in RA were similar to C, whereas DHEA secretion after ACTH testing was significantly (p<0.01) reduced. During HPA challenge, F responses in PMR patients proved inadequate in the setting of the inflammatory status, confirmed by increased IL-6 levels. In addition, these patients showed significantly (p<0.05) increased 17-hydroxyprogesterone (17-OHP) responses after ACTH testing as compared to C. The longitudinal study in PMR patients showed that glucocorticoid therapy leads to a stable reduction of IL-6 and of acute-phase reactant levels, which persist even after glucocorticoid tapering. Our data show an inadequate adrenal secretion in RA and PMR, both characterized by increased levels of HPA axis-stimulating cytokines. The reduced basal levels of DHEAS in RA might be ascribed to a reduced biosynthesis as consequence of a cytokine-induced impairment of P450 17.20-lyase activity. In PMR, the ACTH-induced enhanced 17-OHP levels suggest a partial age- and cytokine-induced impairment of the P450 21 beta-hydroxylase, which eventually leads to inadequate glucocorticoid production. The clinical and biochemical improvement observed after glucocorticoid therapy in patient with RA and PMR, might thus be attributed to a direct dampening of pro-inflammatory factors as well as to the restoration of the steroid milieu. Given its multifaceted properties, including the ability to counteract the negative side effects of glucocorticoids, the therapeutical administration of DHEA might be considered in these pathologies, provided its safety is proved.