We measured the minimum amount of endogenous dopamine (EDA), necessary for the expression of rotational behavior induced by D2 receptor stimulation in striatal or medial forebrain bundle (MFB) lesioned rats. We correlated these results with the minimum dose of D1 receptor agonists needed to substitute EDA in its permissive role for D2 motor effects to take place. Rats with unilateral quinolinic acid (QA) striatal or 6-hydroxydopamine (6-OHDA) MFB lesions were given increasing doses of the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT) in combination with a fixed dose of the D2 receptor agonist quinpirole (trans-(-)-4aR-4,4a,5,6,7,8,8a,9-Octahydro-5-propyl-1H-pyrazolo(3, 4-g) quinoline hydrochloride) and tested for rotational behavior. The animals were later sacrificed and striata removed; EDA was measured by high performance liquid chromatography (HPLC). Rotational responses were abolished by increasing doses of AMPT inducing a stepwise depletion of EDA. EDA content and rotational behavior to D2 stimulation showed a high degree of correlation. There was an abrupt reduction in rotational behavior at dopamine levels of 50-60% of controls in both animal models. In addition, striatal or MFB lesioned rats which were maximally depleted of dopamine by AMPT pretreatment received a fixed dose of quinpirole and then challenged with increasing doses of a D1 receptor agonist SKF 38393 ((+/-)-1-Phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride). Rotational behavior was restored by SKF 38393 in both animal models in a dose-dependent fashion. Our results confirm the need for simultaneous D1/D2 stimulation in the generation of rotational behavior in both animal models. Moreover, they demonstrate the existence of a threshold level of D1 stimulation necessary to exert its permissive role on D2 mediated responses.