We investigated whether daily oral washings with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) solution improved grade III-IV oropharyngeal mucositis (OM) in patients with hematological malignancies undergoing stem cell transplantation. Forty-one consecutive patients (21 males and 20 females, median age (range) 44 (16-69) years) were prospectively randomized to perform daily mouth-washes with either a 400 microg rhGM- CSF (Molgramostin, Schering-Plough) solution (group A, n = 18) or with a saline solution (group B, n = 23). Primary end-points were the intensity of OM, night rest quality and characteristics of food intake. Secondary end-points were need for and duration of parenteral nutrition, oral and intravenous analgesic requirements, incidence of viral or fungal oral infections and development of neutropenic fever. No differences were found between the placebo and rhGM-CSF-treated groups regarding overall duration of OM, maximum grade, reduction in at least one grade of OM (nine patients (56%) in group A vs 13 patients (68%) in group B), reduction of spontaneous or swallowing-induced pain, improvement in oral food intake, use of parenteral nutrition or use of systemic analgesics. In conclusion, mouth-washings with a 400 microg of rhGM-CSF solution do not improve severe OM in hematological patients undergoing stem cell transplantation.