The experiment described here tests the effect of intracerebroventricular (icv) injection of nitric oxide (NO) precursors, such as L-arginine (L-arg) and nitroprusside (NP), on the thermogenic changes induced by lesion of the lateral hypothalamus (LH). The firing rate of the nerves innervating interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures (TIBAT and TC) were monitored in urethane-anaesthetized male Sprague-Dawley rats lesioned in the LH. These variables were measured before and after an icv injection of 4 mumol L-arg or 400 nmol NP. The same variables were also monitored in: a) lesioned rats with icv administration of saline; b) sham-lesioned animals with icv injection of L-arg or NP; c) sham-lesioned rats with icv injection of saline. The results show that L-arg or NP injection reduces the increases in firing rate. TIBAT and TC induced by LH lesion. These findings suggest that NO plays a key role in the thermogenic changes following LH lesion.