Male mice with high isolation-induced fighting tendencies were administered 200 mug 6-OHDA or vehicle intraventricularly and tested for fighting tendency for up to 10 weeks until sacrifice, and assayed for brain NE levels. A strong correlation was found between NE depletion and reduced fighting tendency after 6-OHDA treatment. The depressed fighting by mice with less than 200 ng. NE/g persisted throughout a series of test fights, indicating no recovery in fighting behavior throughout the survival time.