The authors mapped QTLs associated with locomotor activation and anxiety using 196 female and 166 male F2 mice. The F2 mice were derived from a (C57BL/6J x C58/J)F1 cross and genotyped using a panel of 211 SNP markers, yielding an average SNP density of one marker per 11 mega base pairs. A significant QTL on mouse Chromosome 8 (Lacanx1) is associated with multiple behaviors, including total distance (LOD = 4.1, peak 49 Mb), ambulatory episodes (LOD = 3.8, peak 62 Mb), percent time resting (LOD = 3.5, peak 89 Mb) and average velocity (LOD = 3.3, peak 78 Mb). Two additional QTL that associate with multiple phenotypes were identified. A locus on mouse Chromosome 6 (Lacanx 2)is significant for total distance (LOD = 3.3, peak 47 Mb) and suggestive for both ambulatory episodes (LOD = 2.7, peak 49 Mb) and percent time resting (LOD = 2.8, peak 49 Mb). A QTL on mouse Chromosome 1 (Lacanx 3) (LOD = 3.3, peak 160 Mb) is significantly associated with percent time spent in the center of the open field and suggestive for average velocity (LOD = 2.6, peak 160 Mb).QTL loci that were alsofound to associate with multiple measures, a significant QTL was also identified on mouse Chromosome 13( Lacanx 4) (LOD = 3.6, peak 77 Mb) that associates specifically with percent time spent in the center of the open field.