Design Participants demographic characteristics, psychosocial evaluation, and psychiatric, medical, and drug use histories will be characterized. DNA will be collected via cheek swabs of up to 30 potential participants for determination of dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) gene polymorphisms. Participants (N=16) with suitable polymorphisms will be asked to under go skin biopsies; 2 individuals for each of two genotypes for each gene (DAT or VMAT), i.e., 8 samples from addicts and 8 samples for control subjects. Collaborators at Case Western Reserve University will use the skin cells to derive and characterize patient-specific, induced pluripotent stem (iPS) cells that carry monoamine transporter polymorphisms for the hDAT1 and hVMAT2 genes. They will differentiate patient-specific iPS cells line into dopaminergic neurons and carry out a detailed and functional characterization of these cells to identify their molecular characteristics.