DBA/2 J mice show impaired social behavior. The percentages of social time spent by the DBA/2 J and C57BL/6 J mice in (A) resident-intruder test and (B) three-chambered test are shown (n = 8 per strain). **P < 0.01; ***P < 0.001. Data were analyzed by Student’s t test. Results are presented as mean ± SEM.