We have been investigating brain perfusion in the patients suffering from major depression by single-photon emission computed tomography (SPECT) for several years in Department of Psychiatry in Brno. The principle of SPECT is radionuclide administration to patients and the subsequent target organ uptake of the radiotracer is measured over time. We obtain the information about the physiological process of interest. As for our results SPECT does not seem to be an appropriate diagnostic screening method for depression. Maybe it can be used as tool for the objective treatment reactivity evaluation.