Investigations of cerebral blood flow and metabolism provide interesting data concerning specific brain regions involved in depression. The objective of this paper is to present to Polish readers results of studies using PET in patients with depression. Provocation of transient sadness in healthy subjects during clinical experiments was associated with increase of metabolism in limbic and paralimbic regions and decreased metabolism in dorsolateral prefrontal cortex. During depression metabolism of dorsolateral prefrontal cortex (DLPF) was decreased but metabolism of subgenual cingulate was increased. After recovery, normalisation of metabolism, that is increase in DLPF was observed in patients treated with antidepressive drugs as well as psychotherapy. These data point to the role of frontal-thalamic-limbic circuits in regulation of emotions and pathogenesis of depression.