🔖 The oropharyngeal aerobic gram-negative bacillary carriage, uncommon in healthy people, is high in patients with head and neck cancer. A marked increase in oral Gram-negative enterobacteria and pseudomonads has particularly been shown during the period of radiation therapy. Irradiation-induced oral mucositis in patients with cancer of the head and neck is associated with changes in this oropharyngeal microflora, but this change is very unlikely to be a causative one. The aim of the study was to ascertain whether there was any change in the Gram positive and Gram negative oropharyngeal flora and to objectively determine whether these bacteria could play a role in the causation of irradiation mucositis.