This study determined the effects, in the rat, of 8-day treatment with arginine-aspartate on haloperidol-induced catalepsy, decrease of locomotor activity and change of striatal dopamine, homovanillic acid (HVA) and dihydroxy-phenylacetic acid (DOPAC) content. Arginine-aspartate was able to attenuate the haloperidol-induced decrease of locomotor activity and to significantly reduce the catalepsy. Moreover, arginine-aspartate treatment itself increased striatal dopamine content and produced a significant decrease of the HVA/dopamine ratio. Pretreatment with arginine-aspartate was able to partially counteract the haloperidol-induced changes of dopamine metabolism: the haloperidol-induced increases of the DOPAC/dopamine and HVA/dopamine ratios were significantly reduced in arginine-aspartate- pretreated rats. These results suggest that the action of arginine-aspartate on haloperidol-induced neurobehavioral effects is probably mediated by interference with striatal dopaminergic innervation.