505 mice of BB and C 57 BL/6 as parental strains, as well as derived F 1, F 2 and backcrosses were tested for spontaneous motor activities and eliminations in 4 different apparatus. A component being highly associated expecially with open-field measures was obtained from the principal component analysis. This suggests that an individual score on this composite variable represents a certain unique open-field behavioral pattern. Relatively low heritabilities in broad sense (coefficient of genetic determination) were given by classic genetic analysis, indicating the substantially great effects of the environmental factors of this behavioral character. Further, albino mice in BB, F 2 and B X B showed a very inactive open-field behavioral pattern than pigmented mice.