The selective dopaminergic antagonist ligands [ 3H]SCH 23390 and [ 3H]sulpiride were used to reveal autoradiographically dopamine D 1 and D 2 receptors, respectively, in brain sections from rats which had received unilateral 6-hydroxydopamine (6-OHDA) injections destroying ascending nigrostriatal neurones. The binding of both ligands to striatal sections was first shown to be saturable, reversible and of high affinity and specificity ([ 3H]SCH 23390: B max 2.16pmol/mg protein, K d 1.4NM; [ 3H]sulpiride; B max 0.67pmol/mg protein, K d 10.7nM). After unilateral stereotaxic 6-OHDA injections, rats rotated contralaterally when challenged with apomorphine (0.5 mg/kg), or specific D 1 or D 2 agonists, SKF 38393 (1.0–5.0 mg/kg) and LY 171555 (0.05–0.5 mg/kg), respectively. Loss of forebrain dopaminergic terminals was assessed autoradiographically using [ 3H]mazindol to label dopamine uptake sites. A loss of approximately 90–95% of uptake sites was reproducibly accompanied by an enhanced density of binding ipsilaterally for the D 2 ligand, [ 3H]sulpiride, in all areas of the striatum, but most markedly in the lateral areas. An increase in the D 2 binding site density was also seen in the ipsilateral nucleus accumbens and the olfactory tubercle. In contrast, in the same animals, the striatal D 1 receptors were far less affected by dopaminergic denervation, with no consistent changes seen in the binding of [ 3H]SCH 23390. These results suggest that dopamine D 2 receptors are more susceptible than D 1 receptors to changes after dopaminergic denervation, which is expressed as an increase in the density of binding sites revealed here with [ 3H]sulpiride.