The present study analyzes the effects of baclofen (BAC) on mice brain neurochemical alterations during the morphine (MOR) withdrawal syndrome. Male Swiss-Webster albino mice (27-33 g) were rendered dependent by intraperitoneal (i.p.) injection of MOR (2mg/kg), twice daily for 9 days. On day 10, the dependent animals were divided into two groups: one receiving naloxone (NAL; 6 mg/kg i.p.) to precipitate the withdrawal syndrome 60 min after the last dose of MOR and the other received BAC (2mg/kg, i.p.) followed by NAL (6 mg/kg, i.p.), injected 30 and 60 min after the last dose of MOR, respectively. Ten minutes after these treatments, mice were killed by decapitation and the striatum, cortex and hippocampus were dissected to determine endogenous concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT) and their metabolites using HPLC with electrochemical detection. Striatal DA, dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) concentrations as well as cortical DA concentrations of the withdrawal groups decreased significantly with respect to the control groups. BAC attenuated the decrease in DA and DOPAC concentrations observed during the withdrawal, without modifying per se the control DA concentrations. No changes on 5-HT and its metabolite 5-hydroxyindolacetic acid (5-HIAA) concentrations were observed during the MOR abstinence syndrome. The prevention caused by BAC on the decreased concentrations of DA induced by MOR withdrawal could have a therapeutic interest for the management of withdrawal syndrome.