An anxiety-related behavior is an emotional response of an organism, which is quantitatively measured by several behavioral paradigms. We employed two most frequently used behavioral tests, the open field and light-dark exploration. to comparatively analyze the anxiety-like behaviors in four inbred mice. For an accurate recording of movement, motion analysis software was de eloped that acquires a real-time video input to generate a behavioral path. Effects of the strains on the test results were evaluated by ANOVA with the Newman-Keuls post hoe comparison. Eight different behavioral indices, four from each tests, were grouped into two classes the results of duration, center crossing, transition, rearing. and ambulation indicate strain differences of FVB/N > C57BL/6J greater than or equal to BALB/cA greater than or equal to CBA/N (1), while stretched-attend posture. peeping. and defecation show, the tendency of FVB/N = C57BL/6J < CBA/N less than or equal to BALB/cA (H). The peeping is a novel type of behavior observed in this work. Although there is a variation among behavioral indices in their discrimination between inbred lines. the behaviors are highly correlated one another such that each class I or class 11 behaviors are clustered on two orthogonal factor planes as a result of the principal component analysis. The polarization of each inbred line toward these two behavioral biases may reflect genetic backgrounds of these strains. (C) 2002 Elsevier Science B.V. All rights reserved.