This study seeks to examine dopamine (DA) transmission in vivo, using positron emission tomography (PET) with \[C-11\]FLB 457, in cortical regions of interest in subjects who have a history of cocaine dependence. We hypothesize that cocaine dependence is associated with decreases in dopamine in the prefrontal cortical regions compared to controls. This may explain the impulsivity and cognitive deficits that underlie relapse in this disorder.