Radiation-induced esophagitis often results in treatment interruption, which may severely affect the probability of control of the local disease in patients undergoing chest radiotherapy (RT). No effective regimen that would reduce the incidence and severity of this complication has been identified up to now. Although acceleration of oral mucosal healing using topical recombinant human granulocyte macrophage colony-stimulating factor (rhGM-CSF) has been reported, the mechanism of such an interaction remains obscure. Effective topical application of rhGM-CSF for the treatment of radiation-induced esophagitis has never been reported in the past. In pharmacological studies, we observed that glycerol exerts a remarkable stabilizing effect on rhGM-CSF immunoreactivity. After studying the kinetics of esophageal emptying with nuclear imaging, we proposed a rhGM-CSF regimen that could be applied for topical treatment of esophagitis during RT. The regimen was applied for 5 consecutive days in a cohort of 36 patients undergoing chest RT, immediately after the documentation of grade 3 esophagitis. RT was not interrupted. Mucosal biopsies were performed endoscopically and examined immunohistochemically. Regression of dysphagia to grade 0/1 was observed in 19 of 36 (52%) patients, whereas grade 2 dysphagia persisted in 12 of 36 (33%) patients. Progression of dysphagia was seen in 5 of 36 (14%) patients. Recurrence of severe esophagitis within 5-8 days after rhGM-CSF therapy was observed in 7 of 31 (22%) patients with initial response to rhGM-CSF. Four of these patients presented significant improvement of symptomatology after additional rhGM-CSF medication. In immunohistochemical studies, active intraepithelial neovascularization and thymidine phosphorylase and vascular endothelial growth factor overexpression were observed in the damaged epithelium, which was not accompanied by macrophage or neutrophil infiltration. We conclude that rhGM-CSF topical therapy (p.o. administration) exerts a significant therapeutic effect against RT-induced esophagitis. The rhGM-CSF mucosa healing effect is probably due to its direct angiogenic activity and/or to the potentiation of the activity of other angiogenic factors released by the damaged epithelium.