3-amino-4-(2[11C]methylaminomethylphenylsulfanyl)benzonitrile (DASB C-11) exhibits excellent in vitro and in vivo properties toward the serotonin transporter. Parametric imaging of serotonin transporters (SERT) with DASB C-11 PET is a useful data analysis tool. DASB C-11 is a suitable PET radioligand for measuring drug occupancy of the SERT in vivo and has potential for monitoring in vivo changes in serotonin levels. Studies in humans showed that the regional distribution of DASB C-11 uptake was concordant with the known densities of SERT sites in the brain. The highest levels of radioactivity were observed in the hypothalamus, intermediate levels were observed in the thalamus and striatum, whereas modest to low levels of radioactivity were observed in the cortical regions and cerebellum, respectively.