Oropharyngeal mucositis occurs in virtually all patients with head and neck cancer receiving radiochemotherapy. The manipulation of the oral cavity microbiota represents an intriguing and challenging target.A total of 75 patients were enrolled to receive Lactobacillus brevis CD2 lozenges or oral care regimen with sodium bicarbonate mouthwashes. The primary endpoint was the incidence of grade 3 or 4 oropharyngeal mucositis during radiotherapy treatment.There was no statistical difference in the incidence of grade 3-4 oropharyngeal mucositis between the intervention and control groups (40.6% vs. 41.6% respectively, p=0.974). The incidence of pain, dysphagia, body weight loss and quality of life were not different between the experimental and standard arm.Our study was not able to demonstrate the efficacy of L. brevis CD2 lozenges in preventing radiation-induced mucositis in patients with head and neck cancer. Although modulating homeostasis of the salivary microbiota in the oral cavity seems attractive, it clearly needs further study.