Numerous animal studies on the correlation between stress and immunity have been performed but few such studies have been made concerning the relationship between various kinds of stress-related emotional behavior and immunological changes. Electrical stimulation of the hypothalamus in cats elicits various emotional behaviors such as restlessness, defensive attack, defensive retreat and quiet biting attack. We examined changes in the lymphocyte proliferative responses and plasma cortisol level which accompanied such emotional behavior. A significant increase in plasma cortisol was observed in the restlessness, defensive attack and defensive retreat groups, but not in the quiet biting attack or non-response (control) groups. A significant increase in the lymphocyte proliferative responses to phytohemagglutinin (PHA) was observed in the restlessness and defensive attack groups but not in the defensive retreat, quiet biting attack or non-response groups. These results suggest that various kinds of emotional behavior appear to be differentially correlated with the lymphocyte proliferative responses, while also being differentially correlated with the plasma cortisol concentration. Because the changes in lymphocyte responses and plasma cortisol did not always completely correlate with one another, the changes in the lymphocyte responses are not considered to be influenced by plasma cortisol alone.