The binding of [3H]-spiroperidol after 4 weeks of hyperglycemia was determined in the rat striatum and anterior pituitary. Alloxan-induced diabetes increased the number of dopaminergic binding sites in the striatum but not in the anterior pituitary. The interaction of metoclopramide with striatal dopaminergic receptors was slightly modified, while that of dopamine, bromocriptine and haloperidol was unaffected. These results suggest that chronic hyperglycemia exerts selective effects on nigrostriatal dopaminergic system in the rat.