The phenotype of genetically modified animals is strongly influenced by both the genetic background of the animal as well as environmental factors. We have previously reported the behavioral and neurochemical characterization of PDE10A knockout mice maintained on a DBA1LacJ (PDE10ADBA) genetic background. The aim of the present studies was to assess the behavioral and neurochemical phenotype of PDE10A knockout mice on an alternative congenic C57BL/6N (PDE10AC57) genetic background. Consistent with our previous results, PDE10AC57 knockout mice showed a decrease in exploratory locomotor activity and a delay in the acquisition of conditioned avoidance responding. Also consistent with previous studies, the elimination of PDE10A did not alter basal levels of striatal cGMP or cAMP or affect behavior in several other well-characterized behavioral assays. PDE10AC57 knockout mice showed a blunted response to MK-801, although to a lesser degree than previously observed in the PDE10ADBA knockout mice, and no differences were observed following a PCP challenge. PDE10AC57 knockout mice showed a significant change in striatal dopamine turnover, which was accompanied by an enhanced locomotor response to AMPH, These studies demonstrate that while many of the behavioral effects of the PDE10A gene deletion appear to be independent of genetic background, the impact of the deletion on behavior can vary in magnitude. Furthermore, the effects on the dopaminergic system appear to be background-dependent, with significant effects observed only in knockout mice on the C57BL6N genetic background.