Mice of the inbred C57Bl/6J strain displayed considerable inter-mice variation in ambulation, rearing, grooming, and defecation in the open-field (coefficients of variation from 30% to 150%). Those differences were not random, because six measurements of the same behavior, taken along six months, were correlated (Kendall coefficients of concordance were in the range 0.37---0.59 and statistically significant); yet, the mice displayed different behavioral profiles along the six measurements (i.e. uniqueness occurred within some order). Of all the behaviors measured, only ambulation and rearing were correlated; i.e., they may constitute a behavioral syndrome.