Mice from 2 inbred strains were exposed either to a postweaning enriched environment or to a standard environment. The design allowed assessment of effects due to environment, genotype, and Genotype X Environment interactions. Environmental enrichment differentially affected hoarding performance in strains. The results also showed that the strains differed in hoarding and that hoarding increased on successive trials. It is suggested that it is important to study both genotype and environment in behavior genetic analyses.