In contrast to the research in panic disorder, not much neurobiological studies have been conducted in social phobia. In challenge-tests using lactate or pentagastrin general anxiety and anxiety symptoms were induced in social phobies, although not as frequent is in panic disorder patients, but no specific social phobic anxiety was induced. The role of neurotransmitters such as serotonin, dopamine and noradrenalin is, as yet, unclear. There are no indications for abnormal hypothalamic-pituitary-adrenal-axis activity or abnormal hypothalamic-pituitary-thyroid-axis activity in social phobia. To the present, preliminary findings in neuroimaging studies show no differences between patients and controls, except a possibly diminished and reversible metabolic activity.