radiosensitization of e coli br by arylhydrazonopropanedinitriles several arylhydrazonopropanedinitriles and an arylhydrazonopropanediethyl ester derivatives of wellknown uncouplers of oxidative phosphorylation have been studied with respect to their ability to radiosensitize e coli br under oxic and hypoxic conditions of the compounds studied 2carboxyphenylhydrazonopropanedinitrile and 2carboxyphenylhydrazonopropanediethylester were found to be the most efficient radiosensitizers under hypoxia whilst the former compound was also found to provide radiosensitization under oxic conditions increased radiosensitization by 4carboxyphenylhydrazonopropanedinitrile was observed on decreasing the ph of the irradiation incubation medium the results are discussed with respect to the physicochemical properties of these compounds and their reactivity with thiols for which data are presented