Randomized controlled clinical trial has been carried out in the Oncology Center in Warsaw and Medical Academy in Lódź to assess the effectiveness of application of Metronidazole as radiosensitizer of hypoxic cells in patients with squamous cell laryngeal cancer treated by Cobalt60 irradiation in the years 1982-1986. Clinical estimation has been obtained by comparison of the effectiveness of four selected methods of dose fractionation (conventional, dynamic, dynamic with Metronidazole, irradiation twice a day) in which NSD and TDF have been comparable (1950, 116). Metronidazole has been applied intraorally six times for a total treatment with 6 g doses. The tolerance of the drug has not been very good: 72% of patients has nausea and/or vomiting. No other side effects have been observed. Major mucosal reactions appeared in patients in which the dose have been fractionated by non conventional method (large fractions, twice daily irradiation). No statistically significant differences in the immediate effect of the radiotherapy and 3 year survival among the groups of patients treated by investigated methods have been found.