ABSTRACT Oxytocin and vasopressin are key effectors of social behaviour (Insel, T. R. and Fernald, R. D. (2004). Annu. Rev. Neurosci., 27: 697-722). Oxytocin effects in humans were recently demonstrated by a behavioural study showing selectively increased trust after hormone administration (Kosfeld, M., et al. (2005). Nature, 435: 673-676). Since this suggested involvement of the amygdala, which is linked to trust (Winston, J. S., et al. (2002). Nat. Neurosci., 5: 277-283) - presumably because of its role in danger monitoring - and highly expresses oxytocin receptors (Huber, D., et al. (2005). Science, 308: 245-248), we studied amygdala circuitry after double-blind crossover intranasal application of placebo or oxytocin (Kirsch, P., et al. (2005). J. Neurosci., 25: 11489-11493). Oxytocin potently reduced amygdala activation and decreased coupling to brainstem regions implicated in autonomic and behavioural manifestations of fear, indicating a neural mechanism for the effects of oxytocin in social cognition in humans and providing a potential therapeutic approach to social anxiety currently being tested in social phobia and autism. Furthermore, these data suggested a translational genetic approach. Preliminary findings (data not presented) from our laboratory using imaging genetics indeed implicate genetic variants for both AVPR1A, encoding the primary receptor of vasopressin in brain, and the oxytocin receptor, OXTR, in amygdala regulation and activation. Taken together, our results indicate neural mechanisms for human social behaviour mediating genetic risk for autism through an impact on amygdala signalling and provide a rationale for exploring therapeutic strategies aimed at abnormal amygdala function in this disorder and in social dysfunction in general.