A considerable effort has been made recently for the development of effective regimens in radiotherapy that would allow the sensitizaion of the radioresistant hypoxic tumor ce1ls. l Among the chemical sensitizers tested so far from a variety of available nitroheterocyclic compounds, metronidazole, a 5-nitroimidazole derivative, and misonidazole, a 2- nitroimidazole analogue, have been found to be particularly promising in view of their ...