A study was carried out on the agonistic behavior of the male volcano mouse, Neotomodon alstoni, with 50 pairs of males which were classified as possible dominants (D) and subordinates (S), utilizing Melzack-Thompson's Method. The aggressiveness levels exhibited by this mouse were recording in the combinations: D vs. D and S vs. S. Two groups were formed: Group I with 12 pairs of D males and 13 of S males, and Group II with 11 pairs of D males and 14 of S males. In Group I the aggressiveness level was quantified after one week of mating and after another week of isolation, and in Group II the sequence of observation was inverted. The aggressiveness level was measured by the number of attacks per hour, an attack being defined as the aggressive physical contac of an animal (aggressor) with another (attacked). The kinds of behavior registered, including offense, defense, and submission patterns, revealed hierarchic relationships. Dominance was correlated significatively (p < 0.05) with a higher level of aggressiveness.