In an interdisciplinary research project involving psychology, behavioral pharmacology psychiatry, genetics and neuroimaging the investigators propose to investigate the therapeutic efficacy of combining an exposure-based cognitive-behavioral group therapy (CBGT) with hydrocortisone treatment. The investigators hypothesize that hydrocortisone exerts both acute beneficial effects by reducing fear during exposure, and long-term beneficial effects by facilitating the extinction of phobic fear. Furthermore, the investigators hypothesize differential treatment responses depending on genetic variations in glucocorticoid-related genes (substudy 1). These hypotheses will be tested in a clinical study with 100 patients with mainly speech anxiety who fulfill DSM-IV criteria for a diagnosis of social phobia and 60 patients with spider phobia.