C57Bl/6J mice displayed considerable inter-mice variation in some behaviors in the open-field and the elevated plus-maze (coefficients of variation from 30% to 200%). Those individual differences were not entirely random, because four successive measurements of each behavior were positively correlated. Application of the aggregation principle revealed that (i) in males and females, odd-even correlation coefficients for ambulation (in the open-fieldand in the plus-maze) were of the order of 0.60, (ii) the odd-even correlation coefficient for defecation in the open-field was 0.74 for males and 0.23 forfemales (not significant), (iii) the odd-even correlation coefficient for the antibody response (to immunization with aggregated bovine serum albumin) was 0.43 for males and 0.60 for females. In males, but not in females, these variables were intercorrelated: ambulation in the open-field, ambulation in the enclosed arm of the plus-maze, and defecation in the open-field; the antibody response was uncorrelated with behaviors.