The selective serotonin reuptake inhibitor (SSRI) fluvoxamine has been used in an attempt to understand whether there is a biological distinction among anxiety disorders. A comparison of fluvoxamine with the specific noradrenaline reuptake inhibitor maprotiline in patients with panic disorder showed fluvoxamine to be a potent anti-panic agent, whereas maprotiline had no effect on the frequency of panic attacks. This result supported the hypothesis of serotonergic involvement in the pathogenesis of panic disorder. In a second study, unlike fluvoxamine, the 5-HT2A/2C antagonist ritanserin had no effect on the number of panic attacks, or phobic avoidance. This suggested that the efficacy of antidepressants in panic disorder was not a result of down-regulation of postsynaptic 5-HT2 receptors. Most studies suggest that the efficacy of antidepressants in obsessive-compulsive disorder (OCD) is not related to their antidepressant or mood-enhancing effects. Fluvoxamine has also been shown to reduce general and phobic anxiety in social phobia patients. In conclusion, serotonergic systems are implicated in the pathophysiology of global anxiety irrespective of the nosological background, and SSRIs, exemplified by fluvoxamine, appear to be effective in panic disorder, OCD and probably also social phobia.