The augmentation effect of (-)pindolol as used in combination with SSRI to treat major depression has been ascribed to blocking of dorsal raphe nucleus cell body 5-HT autoreceptors. In this study, the radioligand [carbonyl-11C]WAY-100635 and positron emission tomography were used to establish whether pindolol at a clinical dose level (10 mg s.o.d.) occupies 5-HT1A receptors in the human brain in vivo. Three healthy males were recruited and each subject was used as his own control. The 5-HT1A receptor occupancy was calculated for the frontal and temporal cortex and the raphe nuclei, using and a ratio analysis with the cerebellar cortex as the reference region. Maximal pindolol plasma concentration was reached within 3 h after drug administration. Two hours after pindolol administration, the regional 5-HT1A receptor occupancy was within the range 7-21% in the three subjects. The study confirms that the 5-HT1A-receptor may be a clinically significant target for pindolol.