The distribution of blood group substances A, B, H, Le-a and Le-b in normal and neoplastic salivary gland tissue was evaluated by means of immunohistochemistry. The serological ABH blood group status of one third of the patients was known. Lewis blood group and secretory status were not known. In normal tissue, expression of blood group antigens corresponded to the serological blood group. Blood group substance H was present in almost every gland, regardless of the serological blood group. In submandibular glands, Le-b was rather selective for mucous acini. In tumors, a relationship of blood group expression to a glandular pattern and a high differentiation could be observed. Blood group substances were expressed at a high level in benign and highly differentiated malignant tumors. In poorly differentiated malignant tumors, they were mostly absent. Blood group expression evaluation could be of value in establishing the level of functional differentiation in salivary gland tumors.