A series of compounds in which a 2-nitroimidazole is linked to a DNA intercalating phenanthridine moiety has been synthesised. Previously, three such compounds, termed nitroimidazole-linked phenanthridines or NLPs, were tested in vitro and showed a greatly enhanced molar efficiency as hypoxic cell radiosensitisers and cytotoxins compared with the untargeted 2-nitroimidazole, misonidazole. Since the cytoxicity of these compounds was shown to be inversely proportional to linker chain length while radiosensitising ability was dependent of it, compounds with five and six carbons in the chain were synthesised in an attempt to lower the toxicity of the drugs while increasing their ability to 'scan' DNA for target radicals. These compounds and a comparison series of n-alkylated phenathridinium ions have been characterised and evaluated in vitro using Chinese hamster ovary and V79 cells and their effects compared with misonidazole. Based on in vitro results, one member of the series was selected and evaluated in vitro using a V79 spheroid tumour model and in vivo using an SCCVII transplantable tumour system. These studies have demonstrated the potential utility of this class of compound.