Caveolins are coat proteins of caveolae, the plasmalemmal transport vesicles. To our knowledge their presence in the human pituitary and various types of hypophysial adenomas has not been investigated. In the present work, expression of caveolin-1 and caveolin-2 was studied by immunohistochemistry using the streptavidin-biotin-peroxidase complex method. The material included 7 autopsy obtained, 5 surgically removed non-tumorous pituitaries, and 97 hypophysial adenomas classified on the basis of histologic immunohistochemical and ultrastructural features. No immunoreactivity was seen for caveolin-1 and caveolin-2 in non-tumorous adenohypophysial and neurohypophysial cells and in the tumor cells, indicating that caveolins are not involved in the initiation and progression of pituitary adenomas. The expression of caveolin-1 and caveolin-2 in the endothelial cells did not depend on age, gender, endocrine status of the patients, morphologic features, and type of pituitary tumors. Scattered endothelial cells were immunopositive for both caveolins showing similar cytoplasmic localization. Evidence that the two caveolins were indeed localized to the same endothelial cell was demonstrated on consecutive sections using Factor-8 and CD-34, two reliable endothelial cell markers. Not every endothelial cell was immunoreactive for the two caveolins, suggesting that the functional status of endothelial cells is not the same within the adenomas, not even in the same capillary.