Antiserum prepared against highly purified glucocorticoid receptor was used for immunocytochemical studies. Rat liver and pituitary were chemically fixed, and histological sections were examined for immunoreactivity by an indirect immunoperoxidase procedure. In liver, immunoperoxidase staining was observed in the nuclei and cytoplasm of most hepatocytes. Kupffer, endothelial, and bile duct cells were not significantly stained. Control sections treated with preimmune serum remained unstained; preadsorption of antisera with purified liver glucocorticoid receptor resulted in a significant decrease in immunocytochemical staining. In adrenalectomized rats, nuclear staining was markedly reduced, whereas in adrenalectomized rats treated with cortisol acetate, the density of nuclear staining was comparable to and often slightly higher than that in intact animals. In the anterior pituitary, numerous cells were immunoreactive; their nuclei, cytoplasm, or both were stained. Alternate histological sections to those stained with antireceptor antibodies were processed for the localization of ACTH. It was found that the number of anterior pituitary cells that stained with the antireceptor antibodies exceeded the number of corticotrophs. Cells of the intermediate lobe pituitary were devoid of staining, whereas cells in the posterior lobe were stained. The presence of immunoreactive glucocorticoid receptors in pituitary cytosolic fractions was biochemically confirmed by immunoadsorption studies with [3H]triamcinolone acetonide-receptor complexes. This morphological localization of glucocorticoid receptor in liver and pituitary tissues demonstrated that immunocytochemistry can be successfully used to study localization of the glucocorticoid receptor. The known lack of response of intermediate pituitary cells to glucocorticoid may be secondary to a very small number or even an absence of glucocorticoid receptors.