We have previously shown that a single dose of intravenous citalopram in healthy volunteers enhances the detection of fearful facial expressions, suggesting an effect of acute selective serotonin re-uptake inhibitor (SSRI) treatment on the processing of anxiety-related stimuli. The aim of the present study was to confirm and extend this finding by studying the effects of a single dose of oral citalopram on a range of tasks designed to assess different aspects of emotional processing. A total of 32 healthy volunteers were randomly allocated to double-blind treatment with either citalopram 20 mg orally or placebo. Participants then completed a series of tasks assessing emotional aspects of attention (visual-probe task), perception (categorization of facial affect), memory (emotional memory task) and reactivity to threat (emotion potentiated startle). Relative to placebo-treated subjects, participants treated with citalopram demonstrated improved recognition of fearful faces and increased baseline startle response. However, the citalopram group also showed an attentional bias towards positive words. Our data suggest that acute oral citalopram increases the processing of anxiety-related stimuli in healthy volunteers. This mechanism could underlie the known tendency of SSRIs to increase anxiety in patients early in treatment. Our data also suggests that some of the positive biases in emotional processing produced by SSRI treatment might be detectable at the beginning of treatment.