A series of 1-alkyl-3-nitro-1,2,4-triazoles has been prepared and assessed in vitro as radiosensitizers of hypoxic cells and as bioreductive cytotoxins. The differential hypoxic:aerobic cytotoxicities of representative compounds have been determined and compared with analogous 2-nitroimidazoles. It is found that the 3-nitrotriazoles are considerably less effective than the corresponding 2-nitroimidazole derivatives. This result includes dual-function nitrotriazoles where potential alkylating moieties have been incorporated into the molecule. In contrast, the 3-nitrotriazoles show similar or slightly improved radiosensitizing efficiency, in accord with their redox behaviour, and significantly lower chronic aerobic toxicity compared with the corresponding 2-nitroimidazoles. On the basis of a derived in vitro therapeutic ratio, 1-(3-nitro-1,2,4-triazol-l-yl)-3-piperidino-2-propanol (8) has been identified as particularly active and warrants further evaluation as a hypoxic cell radiosensitizer in vivo.