Tube-dominance behavior differed significantly in C57BL/6By and BALB/cBy mice. Evaluation of these two inbred strains, and their recently developed recombinant inbred strains permitted the derivation of an hypothesis regarding possible genetic control of this behavior in mice. The results were analyzed by means of patristic matrices with accompanying phylogenetic tree analysis that marks the first occasion that such analysis has been used for a behavioral trait. Based on the data obtained and the statistical analyses and groupings of the various strains, the most satisfactory hypothesis that can be proposed at this time is one which assumes that dominance behavior, as measured in this experiment, is influenced genetically by at least 3 loci. Attempts to link these loci were not successful.