In an open study, the efficacy of povidone-iodine in the prophylaxis of mucositis during antineoplastic radiochemotherapy was determined. 40 patients were randomly assigned to a treatment or control group (each 20 patients). All patients received standard prophylaxis of mucositis with nystatin, dexpanthenol, rutoside and immunoglobulin. In addition, the patients of the treatment group performed 4 times daily rinsing with povidone-iodine, the control patients with sterile water. Clinical examination of the oral mucosa was performed weekly during the radiation period and up to 6 weeks after the end of therapy. Oral mucositis was observed in 14 patients of the treatment group (mean grading: 1.0) and in all 20 patients of the control group (mean grading: 3.0). The mean onset of mucositis was after 2.25 weeks in treatment patients and 1.5 weeks in control patients. The mean total duration of mucositis was 2.75 weeks in treatment patients and 9.25 weeks in control patients. The mean AUC values were 2.5 in treatment patients and 15.75 in control patients. All findings were statistically significantly different between the two groups. It is concluded that rinsing with povidone-iodine reduces the incidence, severity and duration of oral mucositis during antineoplastic radiochemotherapy.