In a placebo-controlled double-blind study design, patients will be randomly assigned to receive CBGT + hydrocortisone (Social Phobia: N=50 / Spider Phobia: N=30) or CBGT + placebo (Social Phobia: N=50 / Spider Phobia: N=30). Psychopathological symptoms and stress reactivity will be assessed by psychometric and endocrine parameters before, during and after CBGT therapy. The patients have further the possibility to attend to a neuroimaging study, in which the investigators examine and localize the anxiolytic effect of acute glucocorticoid administration in the brain (substudy 2). In this substudy 2 the investigators compare the patients with social phobia with patients with specific spider phobia and healthy controls as they did in their previous studies (Soravia et al. 2006).