Administered independently, the selective D-1 and D-2 agonists SKF 38393 and LY 171555 elicited dose dependent increases in complex motor behaviors such as locomotion or grooming. Typical stereotypic behaviors were observed only when these agents were combined and only at the higher doses of the D-1 agonist. AMPT pretreatment blocked the effects of the agonists administered independently, but all classes of behavior could be induced when they were administered in combination. Thus, expression of dopamine agonist induced behaviors requires concurrent activation of D-1 and D-2 receptors; the nature of the behavior appears to depend upon the ratio of D-1 to D-2 receptor activation.