Serotonin (5-hydroxytryptamine, 5-HT) is implicated in the aetiology and treatment of a variety of psychiatric disorders. A limitation of research has been the necessity to use indirect measures of 5-HT function. METHOD: We describe a method of analysing pharmacoMRI data using SPM and apply it to the direct i.v. infusion of selective 5-HT reuptake inhibitor, citalopram, in 12 healthy volunteers. Scanning took place on a 1.5-T Philips MRI scanner. RESULTS: Areas implicated in depression and its treatment were observed to have increasing signal with respect to time. These areas included the caudate, the amygdala, the hippocampus, the striatum and the thalamus. CONCLUSION: Direct pMRI using i.v. citalopram opens new ways of investigating 5-HT mechanism in depression and its treatment.