Therapeutic application of immunoglobulin is reported to be successful in radiation-induced oral and oropharyngeal mucositis. In this study the efficacy of prophylactic application of immunoglobulin was investigated. In 42 patients with head and neck cancer, postoperative radiation treatment or radiation combined with chemotherapy was performed. In 20 consecutive patients, prophylactic mucositis treatment consisted of panthenol (4 x 10 ml/day) and nystatin (4 x 1 ml/day). The 22 following patients received, supplementary to panthenol and nystatin, 800 mg (5 ml) human immunoglobulin intramuscularly once weekly. During the treatment time, the degree of mucositis was examined 3 times a week. The distribution of maximal mucositis degree revealed slightly more severe mucous membrane reaction in the control group compared with the immunoglobulin group (n.s.). The analysis of mean mucositis degrees in both groups demonstrated statistically significant differences (t test, p = 0.031) related to the entire group (n = 42) and to those 16 patients receiving radiation combined with chemotherapy. There was no significant immunoglobulin-induced effect on mucositis in patients treated by radiation alone. The time from the beginning of therapy to the first interruption could be prolonged 5 days in the immunoglobulin group (n.s.). In conclusion, it is demonstrated that the prophylactic application of immunoglobulin seems to lower the degree of radiation-induced mucositis. In comparison to the published data about therapeutically given immunoglobulin, the clinical efficacy of the prophylactic application of immunoglobulin as it is performed in this study is less evident.