1. Central injection of a long lasting enkephalin analog (D-Ala2-leu-enkephalin-amide) produced a syndrome of stereotyped motor activity. 2. This activation syndrome was significantly reduced by two dopamine (DA) blockers (pimozide, fluspririlene) and by an agonist of inhibition-mediating DA receptors [(3,4-dihydroxyphenylamino)-2-imidazoline]. 3. Intact DA functioning is necessary for the occurrence of this enkephalin-mediated behavioral syndrome.