 2. To address one of the criticisms raised by the CSRP review, namely 1 to quantify SERT binding parameters with 11CDASB in up to 10 normal subjects and 2 to determine the reliability and reproducibility of SERT binding parameter measurements by performing a second retest 11CDASB PET study in the same subjects, because such data are not available for this radioligand. PET scanning will be performed with an intravenous injection of 20 mCi of 11CDASB for 2 h, during which multiple arterial blood samples will also be obtained. The reproducibility of SERT binding parameters will be assessed by calculating the variability as well as the intraclass correlation coefficient between testretest measurements. We expect that 1 we can accurately quantify SERT binding parameters using 11CDASB PET imaging and 2 11CDASB PET measurements of SERT binding will be reliable and reproducible. 