The lateral habenula is a major station conveying information between the limbic forebrain and midbrain. Bilateral lesions of the lateral habenula were found to increase exploratory behavior, including locomotor activity, rearing and hole-poke responses in rats. These effects were not due to an augmentation of general motor function, since the animal's performance on the Rota-rod treadmill was not significantly changed by the same manipulation. Lateral habenular lesion was also found to potentiate the effects of footshock stress on exploratory behavior in an open field. It is suggested that the lateral habenula probably plays an inhibitory role in the expression of certain emotion-related behaviors under normal and stressful situations.