Fifty-four adenoid cystic carcinomas (ACC) arising in major and minor salivary glands as well as in normal salivary glands were studied by immunohistochemistry for the presence of vimentin, neuron-specific enolase (NSE), alpha 1-antichymotrypsin (alpha 1-ACT) and alpha 1-antitrypsin (alpha 1-AT). Five patterns of histological differentiation were found in ACC, and for the cellular components of each, it was possible to establish a special immunohistochemical profile. In ACC, vimentin-positive cells were observed in the outer tubular, cyst-lining and small angular cells. NSE was positive in the myoepithelial cells of normal salivary gland. Neoplastic cells of ACC showed NSE positivity mainly in the small angular cells and partly in the duct luminal cells. alpha 1-ACT was localized in the intercalated duct cells and serous acinar cells of normal salivary gland, and in the duct luminal cells of ACC. alpha 1-AT could not be detected in any of the epithelial cells of normal salivary gland. In ACC, eosinophilic hyaline material in the cribriform spaces was positive for alpha 1-AT, but no positivity was demonstrated in tumor cells. The present study showed that there are at least two populations of tumor cells in ACC: duct luminal cells that express alpha 1-ACT, thus indicating their ductal character, and small angular cells that express vimentin, characteristic of non-luminal cells. Moreover, our results indicate that alpha 1-AT is a useful marker of basement membrane-like material.