The amygdala has long been thought to be involved in emotional behaviour(1,2), and its role in anxiety and conditioned fear has been highlighted(3,4). Individual amygdaloid nuclei have been shown to project to various cortical and subcortical regions implicated in affective processing(5-7). Here we show that some of these nuclei have separate roles in distinct mechanisms underlying conditioned fear responses. Rats with lesions of the central nucleus exhibited reduction in the suppression of behaviour elicited by a conditioned fear stimulus, but were simultaneously able to direct their actions to avoid further presentations of this aversive stimulus. In contrast, animals with lesions of the basolateral amygdala were unable to avoid the conditioned aversive stimulus by their choice behaviour, but exhibited normal conditioned suppression to this stimulus. This double dissociation demonstrates that distinct neural systems involving separate amygdaloid nuclei mediate different types of conditioned fear behaviour. We suggest that theories of amygdala function should take into account the roles of discrete amygdala subsystems in controlling different components of integrated emotional responses.