An earlier study (Borg et al., Am J Psychiatry 2003) found an inverse correlation between [carbonyl-(11)C]WAY-100635 ligand binding to 5-HT(1A) receptors and scores for self-transcendence, but no other of the six dimensions of the Temperament and Character Inventory, in a group of healthy males. The aim of this study was to investigate if the finding of an inverse correlation between spirituality and 5-HT(1A) could be seen in patients suffering from major depressive disorder or replicated among healthy volunteers. A total of 23 patients with major depressive disorder and 20 healthy volunteers were examined with PET using [carbonyl-(11)C]WAY-100635 as the radioligand. The personality traits were measured using the Finnish version of the Temperament and Character Inventory and correlated with ligand binding (BP). No significant correlations were found between the different Temperament and Character Inventory subscales and BP in any of the studied brain regions (amygdala, anterior cingulate cortex, dorsal raphe nuclei, dorsolateral prefrontal cortex, angular gyrus, inferior, middle, and superior temporal gyri, medial prefrontal cortex orbitofrontal cortex, hippocampus, insular cortex, subgenual anterior cingulate cortex, supramarginal gyrus, ventrolateral prefrontal cortex, and posterior cingulate cortex). These results do not support the idea that the serotonin system forms the biological basis of spiritual experiences among patients suffering from major depressive disorder or among healthy volunteers.