It is well established that the agonistic behavior of offense in mice is heritable. However, few genes have been identified or mapped for offense. For segments of chromosomes with effects on offense, a positional candidate strategy can be used to find such genes. This approach is illustrated for the effect of the male specific part (nonpseudoautosomal region; NPAR) of the mouse Y chromosome on offense. It is proposed that a positional candidate for this effect is Sry. The Sry protein is a transcription factor. Its mRNA is expressed in fetal and adult brain. Its protein binds to response elements in the 5' end of the aromatase and the Fra1 genes. Each of these genes has potential effects on several brain neurotransmitter systems involved in offense. The NPAR Y chromosomes of several pairs of inbred strains have differential effects on offense. This hypothesis would be tested by sequencing Sry for some of these pairs of strains.