['Deficiencies in serotonin function have been associated with irritability and aggression but enhancing serotonin has also been shown to promote social status and affiliative behaviour in non-human primates and more recently in humans.', 'To investigate the effects of citalopram, a selective serotonin reuptake inhibitor (SSRI), on social behaviour with a flatmate and a stranger.', 'Ten pairs of healthy volunteers took part in a randomized double-blind crossover study of 2 weeks treatment with citalopram (20 mg/day) and placebo with a 2-week washout period. In each pair, one person (subject) took the tablets and the other (flatmate) received no treatment. On the last day of each treatment period, the subjects socially interacted with a confederate behaving as a responsive person in a stranger-dyadic social interaction paradigm. After the interaction, subjects played the Mixed-motive game, which measures cooperative behaviour and communication, with the confederate. The flatmates evaluated the social behaviour of the subjects before and at the end of the treatment periods.', 'On citalopram, the subjects were rated as significantly less submissive by their flatmates and they showed a dominant pattern of eye contact in the stranger-dyadic social interaction paradigm. They also reduced the number of points they awarded themselves and sent more cooperative messages during the game.'] Does serotonergic intervention affect both social dominance and affiliative behaviour?