Aggressive behavior between male rats induced by electrical stimulation of the hypothalamus (ESH) is stimulated by androgens. This was demonstrated by recording the changes in threshold current intensities (the amount of current needed to induce attack behavior in 50% of the trials), just before castration, after castration, during subsequent treatment with high doses of testosterone propionate, and finally during oil treatment. The results demonstrate that, to induce the same aggressive responses, in absence of androgens more electrical current is needed than when these hormones are present in the general circulation of the ESH stimulated animals.