The role of the brain catecholaminergic system in establishing dominant-subordinate relationships in mice of different genotypes was studied using inhibitors of tyrosine hydroxylase (alpha-methyl-p-tyrosine) or of dopamine-beta-hydroxylase (FLA-57) or FLA-57 plus the dopamine precursor, DOPA. Demotion in all dominant and subdominant animals was associated with decreased noradrenaline levels, but the aggressive behavior of dominant male mice depended on the noradrenaline/dopamine ratio. Alterations in this relationship seem to have specific effects on social dominance in animals in the micropopulation, as drug-treated mice do not exhibit changes in their general activity. It can be concluded that brain catecholamines are of prime importance in maintenance of dominance.