The experiment was designed to elucidate the question whether the unilateral ablation of the amygdala significantly affects sexual behavior or not. For this purpose, the effect of the unilateral amygdalecto-my upon Matatabi-response was investigated in the cat (R-cat), particularly in cats which showed unmanifested Matatabi-response in the innate status (NR-cat). Following the unilateral damage to the amygdala, NR-cats showed a significant manifestation in their Matatabi-response behavior, while R-cats indicated no change in it, their performance level being the same as preoperatively. It is concluded from the present results that even the unilateral ablation of the amygdala affects sexual behavior significantly, this being in contrast to many previous reprots. The present finding implies that individual differences in sexual behavior appear to depend on the neural basis of the amygdala, supporting an assumption that the amygdala is a controlling center of sexual and emotional behaviors.