OBJECTIVE Irradiation-induced sialadenitis is a significant cause of morbidity in head and neck cancer patients receiving radiotherapy. Neither the exact aetiopathology of chronic irradiation-induced sialadenitis nor the mechanisms leading to atrophy of the glandular cells associated with an increase in extracellular matrix are understood. The aim of our study was to determine the phenotype of the inflammatory infiltrate and to study its distribution in the affected submandibular glands. RESULTS Paraffin-embedded submandibular glands from a homogeneous group of 19 patients with advanced oropharyngeal cancer who received conventional radiotherapy to the primary site and upper neck were analysed. In all patients the radiation dose and field were approximately equal. The submandibular glands were obtained during neck dissection. To characterize the lymphoid infiltrate, all tissue sections were immunostained for T cells (CD3, CD4, CD8), cytotoxic T cells (granzyme B), B cells (CD20), and macrophages (Ki-M1p). A histopathological classification into four grades was established based on the degree of glandular atrophy, fibrosis and lymphocytic infiltration. Phenotypic analysis of submandibular gland sections revealed that the great majority of lymphocytic infiltrates were cytotoxic T cells associated with acinar cell destruction. CONCLUSIONS The significantly elevated frequencies of cytotoxic cells in the submandibular glands of patients with irradiation-induced sialadenitis suggest that cell-mediated immune mechanisms may play a part in the pathogenesis of this disease.