O-Nitrobenzyl and p-nitrobenzyl alcohols, halides, and N-substituted carbamates were prepared as potential bioreductive alkylating agents, and first half-wave reduction potentials of these compounds were measured by differential pulse polarography. The cytotoxicities of these agents were examined by determining the colony-forming ability of EMT6 tumor cells following exposure to each agent at concentrations of 0.01 to 500 microM for 1 h at 37 degrees C under conditions of normal aeration and chronic hypoxia. The o-nitrobenzyl compounds were significantly more cytotoxic to hypoxic cells than to oxygenated cells. This selective cytotoxicity is hypothesized to result from alkylation following more efficacious bioreductive activation of these compounds by hypoxic cells. Nitrobenzyl compounds with such selective toxicity to hypoxic neoplastic cells may prove to be particularly valuable in combination therapy designed for the treatment of solid tumors.