A commonly used animal model for tardive dyskinesia is the oral stereotypy that is expressed by a challenge dose of a dopamine agonist after daily administration of dopamine antagonists (neuroleptics). In the first of two experiments the expression of this dopamine agonist-induced oral stereotypy was prevented by the concomitant administration of the opiate antagonist naloxone. In a second experiment, if the stereotypy was allowed to be expressed, it could be blocked by the administration of naloxone. To the extent that the effects of chronic neuroleptic treatment in rats is a model for tardive dyskinesia, the results suggest that administration of naloxone can both prevent and block the dyskinetic syndrome associated with neuroleptic use.