Rats with bilateral 6-OHDA-induced striatal lesions exhibit altered apomorphine-induced behavior compared to the typical response seen in intact rats. This response is characterized by stereotypic grooming behavior which is transformed to compulsive and intense biting at higher doses. Other agonists, pergolide, bromocriptine, N-n-propylnorapomorphine and L-dopa/carbidopa, caused the same response. Direct intrastriatal infusion of apomorphine after 6-OHDA-induced lesions of the striata also produced this response, while similar SKF 38393 infusion caused more licking than biting, directed at the abdomen instead of the forepaws. The dopamine receptor antagonists haloperidol, SCH 23390 and sulpiride effectively blocked apomorphine-induced behaviors in dopamine-depleted animals. This altered behavior was not observed in rats with dopamine depletion in nucleus accumbens (NAS), nor did additional NAS lesions in rats with existing striatal lesions affect the behavior. Further, high doses of apomorphine (up to 60 mg/kg) failed to induce stereotypic grooming in unlesioned rats. We therefore propose that altered apomorphine-induced behavior is a unique consequence of striatal dopamine depletion and not just an intense form of normal stereotypic activity.