Midbrain raphe lesions in rats (raphe rats) induce aggressive behavior including muricide. A single administration of LiCl (Li) 100 mg/kg to raphe rats produced only 25% of muricide inhibition. However, the inhibitory effect of muricide in raphe rats significantly increased from the 5th day following repeated administration of Li. Chronic Li also inhibited muricide in olfactory bulbectomized (OB) rats. The inhibition of muricide lasted until the next day to some extent. In this point, the effect of Li on muricide is similar to that of antidepressants, but not of neuroleptics. On the contrary, RbCl (Rb) showed a tendency to induce muricide. The single re-administration of Li 100 mg/kg on the withdrawal on the 7th day after repeated administration for 14 days showed a significant inhibition of muricide in raphe rats, unlike that in OB rats. Li also showed a partial prophylactic effect on muricide when Li 100 mg/kg was administered for 1 week before raphe lesions. These results suggest that raphe rats may serve not only as an experimental model of depression, but also as that of manic illness.