The effect of the chemically novel dopaminergic agonist, ciladopa (AY-27,110) was studied on rotational behavior in unilaterally 6-OHDA-lesioned rats and on stereotyped behavior in normal animals during and after chronic treatment. Ciladopa, at a 1.25 mg/kg SC daily dose, was administered for 4 and 6 weeks to the lesioned and normal animals, respectively. This dose was threshold for turning but subthreshold with respect to stereotypy. Both behaviors were evaluated weekly during chronic treatment and biweekly for 11 weeks after its discontinuation in response to doses previously shown to elicit turning and stereotypy. The chronic administration of ciladopa enhanced rotational behavior considerably more and with an earlier onset than stereotypy, although the duration of behavioral supersensitivity after cessation of treatment was the same. These results indicate that behaviors mediated by supersensitive or intact dopamine receptors are differently affected by chronic dopamine agonist treatment. The results are discussed in relation to their potential therapeutic implications and current concepts of agonist-induced supersensitivity.