Abnormalities in dopaminergic neurotransmission have been described in substance abuse and different neuropsychiatric disorders including schizophrenia. [I-123] IBZM is a radioligand that has been widely employed for SPECT imaging of dopamine type 2 and type 3 receptors (D2 and D3, respectively) and fluctuations in levels of endogenous dopamine. [I-123] IBZM SPECT has been used in the SPECT Lab of the Clinical Brain Disorders Branch for several years without adverse effects. Pharmacological effects of IBZM are unlikely due to the minimal amounts used and have not been observed. We propose to use [I-123] IBZM SPECT to explore following questions: 1) Can a previously found relationship between N-acetylaspartate (NAA) measures in the dorsolateral prefrontal cortex and striatal dopamine activity in patients with schizophrenia be replicated and is it also found in normal subjects? 2) Do allelic variants of genes for the dopamine type 2 (DRD2) and type 3 (DRD3) receptors, the dopamine transporter (SLC6A3), or enzymes involved in dopamine biosynthesis (TH) and metabolism (COMT, MAOA) affect D2 receptor availability in vivo?