The injection of endothelin-1 (ET-1) into the dorsolateral periaqueductal gray (PAG) area of freely moving rats at doses from 0.1 to 1 pmol/rat induced rotation along the long axis of the body (barrel-rolling). The pretreatment of this area with L-NAME (N omega-nitro-L-arginine methyl ester, 1 mumol/rat), an L-arginine analogue and a potent inhibitor of nitric oxide (NO) biosynthesis, significantly (p < 0.01) potentiated the duration of the ET-1-induced barrel-rolling. Pretreatment of the PAG area with L-arginine (1 mumol/rat), a precursor of NO, significantly (p < 0.01) decreased the ET-1-induced effects. These preliminary data indicate that the L-arginine-NO pathway exerts a functional antagonism on ET-1 induced barrel-rolling at the level of the PAG area.