1 Cytokines may parallel or regulate the beneficial effects of beta-adrenoceptor antagonist treatment observed in chronic heart failure (CHF) patients. Therefore, this study was performed in order to investigate alterations of cytokine levels in beta-blocker-treated patients suffering from CHF. 2 We investigated plasma cytokine levels in eight healthy controls and 12 CHF patients. The patients were treated with standard medication (CHFstd) or with standard medication and additional beta1-blocker metoprolol (CHFmet). Interleukin-(IL)-1alpha, IL-1beta, IL-1 receptor antagonist (IL-1ra), IL-2, IL-6, IL-8, IL-10, tumor necrosis factor-alpha (TNF), soluble TNF receptor type 1 (sTNF-R1), sTNF-R2, and sCD14 were measured by ELISA. 3 IL-1alpha and IL-1beta were not detectable in any of the tested groups. IL-2, TNF, or sCD14 were not altered as compared with healthy control subjects. CHFstd patients expressed enhanced IL-1ra, IL-6, IL-8, IL-10, sTNF-R1 and sTNF-R2. In CHFmet patients IL-1ra, IL-6 and IL-8 remained at the same level. In contrast, sTNF-R1 levels were significantly reduced, although not to control, whereas the sTNF-R2 and IL-10 were reduced to control levels. 4 The cAMP levels of mononuclear cells--recalculated for the patients included in this study from previous work [Werner et al. (2001). Basic Res. Cardiol., 96, 290]--correlated inversely with the sTNF-R2 data (Pearson, r = -0.46; P = 0.041; Spearman, r = -0.64, P = 0.002). 5 The present data indicate an interaction of the neurohumoral and the cytokine system in CHF patients at the cAMP level. Thus, measurement and correlation of sTNF-R2 and cAMP may provide a tool useful during investigation of beta-blocker therapy.