Changes of serotonin2 (5HT2) receptors have been described in depression, and long-term antidepressant treatment has been shown to decrease the number of 5HT2 receptors. In this study, single photon emission computed tomography (SPECT), with 2-123I-ketanserin as a ligand, was used to investigate 5HT2 receptors in vivo in the brain of depressed patients and normal volunteers. A higher uptake of the tracer was observed in the parietal cortex of the patients, and there was a right greater than left asymmetry in the infero-frontal region of the depressed subjects and not in that of the control subjects. These findings could indicate changes in 5HT2 receptors in major depression.