This program project is concerned with individual differences in behavioral and neurochemical response to cocaine. It is designed to characterize the influence of genetics on the individual cocaine-related processes measured, and on the correlations among them. It will furthermore identify the chromosome regions wherein are located effective genetic loci accounting for as little as 15 per cent of the phenotypic variance. This information will be used to breed selectively to generate lines of animals differing with respect to two of the most influential of these loci and both in combination, with the rest of their genotypes being randomly distributed. These lines will constitute powerful models for investigating the mechanisms underlying the genetic influence.