The effects of the selective cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide-hydrochloride (SR141716A) on extracellular concentrations of norepinephrine and 5-hydroxytryptamine (5-HT) were assessed by in vivo microdialysis in the anterior hypothalamus of freely moving rats. SR14716A (0.3, 1, 3 mg/kg, i.p.) dose-dependently increased norepinephrine efflux to about 300% of baseline, without affecting 5-HT levels. This increase in norepinephrine outflow could play an important role in the pharmacological and potentially therapeutic actions of SR141716A.