Purpose: The aim of the present study was to determine the dose effect of palifermin (recombinant human keratinocyte growth factor, rHuKGF) for reduction of the response of oral mucosa to fractionated radiotherapy in a mouse model. Material and methods: Ulceration (confluent mucositis) of mouse tongue epithelium was analysed as the clinically relevant endpoint. Palifermin at doses from 1-30 mg/kg was administered before the onset (day -3), at the end of the first (day +4) or the second week of irradiation (day +11) with 5 x 3 Gy/week. Each protocol was terminated by graded radiation test (top-up) doses. In a further experiment, optimally effective doses were given on days -3 and +4, or -3, +4 and +11. Results: Single dose irradiation of mouse mucosa yielded an ED50 (dose inducing ulcer in 50% of the mice) of 10.7 ± 1.0 Gy. With fractionated irradiation for 1 week an ED50 for test irradiation (day +7) of 5.1 ± 1.9 Gy was observed. After 2 weeks (day +14), the ED50 was 7.3 ± 1.9 Gy. Palifermin significantly increased the ED50 values in all protocols tested. Maximally effective doses for single injections were 15.0 mg/kg (day -3, +11) or 22.5 mg/kg (day +4), which yielded ED50 values of 12.1 ± 1.3 Gy, 13.7 ± 1.5 Gy and 14.4 ± 1.3 Gy, respectively. Higher palifermin doses did not further increase the ED50. Repeated injections on days -3 and +4 did not increase the ED50 beyond the value obtained with injections on day +4 alone. An additional injection on day +11 increased the ED50 further to 15.1 ± 0.1 Gy. Conclusions: A significant palifermin dose-effect was seen at doses below 15 mg/kg. However, a significant increase in oral mucosal radiation tolerance by palifermin over untreated control tissue was observed already with low doses of 1 mg/kg. This indicates that in clinical studies with palifermin, the dose of the growth factor may be of minor relevance over a wide dose range.